Custom domain email for agencies is a per-zone job, not a shared inbox product. You buy one inbound hop the client can keep when they leave, map named aliases into the inboxes they already use, and refuse leftover MX on every domain you touch. MailerZ is forwarding plus authenticated SMTP. It is not Google Workspace, not IMAP, and not a seat for every freelancer. Free is one domain. Agency is the fleet plan. Confirm numbers on pricing before you quote a retainer.
Quick answer for custom domain email for agencies
Buy one inbound owner per client domain. Publish that MX set alone. Map the addresses the client already prints on invoices. Delete Google, Microsoft, registrar, and parking leftovers the same hour.
Keep the destination inbox the client already lives in. MailerZ is not a new mailbox. Freelancers do not each need a Workspace seat to receive billing@.
Quote the plan against domain count, alias count, seats, store window, and send-as. Free is one domain, ten aliases, fourteen-day store, HOLD unknown, no send-as. Agency is one hundred domains, five hundred aliases, fifty seats, ninety-day store, eight hundred outgoing a month. Confirm the live card.
Authoritative transport stays IETF RFC 5321 — Simple Mail Transfer Protocol. Names stay IETF RFC 1035 — Domain names. Product path: pricing, features, and migration planner.
User problem and decision criteria
Agencies lose retainers on email when two products own MX and nobody can say which hop ate the bank token. The buyer question is not which brand sounds serious. It is who is the exclusive exchanger, who can change TXT, and who cancels the leftover seat.
Decision criteria: client already has Gmail or Outlook; you must not invent a second public identity; leftover MX must be deletable; the hop must show SMTP history; unknown recipients need a written HOLD or reject policy; send-as is optional and paid.
A shared agency catch-all that dumps every client typo into one Slack is not a product. It is a confidentiality incident with a calendar invite. Named aliases per zone, or you do not take the domain.
If the client needs Docs, Meet, and a legal hold inside Google, they still may not need Google MX. Suites and exchangers are different purchases. Do not sell Workspace seats to paper over a forwarding job.
If counsel asked for SOC 2 or HIPAA, stop. MailerZ does not wear those badges. Write that in the proposal. Selling silence is how enterprise deals die in security review.
If the founder wants to keep the old host 'just in case,' that is leftover MX. Price a drain window, not a dual-MX month. Dual MX is a coin flip, not insurance.
Technical mail flow for an agency roster
A sender looks up the client zone. Public NS name a panel. That panel must show only MailerZ MX after cut. The envelope reaches MailerZ. MailerZ rewrites envelope MAIL FROM with SRS and leaves Header From, Subject, Date, Message-ID, body, and MIME alone.
The destination is the human inbox you mapped. Hop history is the proof. Empty history means the probe never arrived. That is leftover MX, wrong NS, or a ghost hosted zone, not a spam-folder mystery.
Unknown recipients follow the plan: HOLD on Free, optional FORWARD on paid. Do not FORWARD a client catch-all into your agency inbox. That mixes tenants.
Send-as is a second job. Copy host, port, and TLS from the dashboard. Do not invent 587. Unauthorized senders get 550 5.7.1. Free cannot send-as. Do not promise founder replies from hello@ on Free.
Self-send from the destination Gmail can short-circuit. Agencies that demo to a client using the client's own Gmail as sender will fail the demo. Use a third mailbox. Every time.
Step-by-step buy path
- List every client zone, public aliases, destination inboxes, and who can change registrar DNS.
- Create a MailerZ workspace. Start free on a lab domain you own. Do not practice on the client's live MX.
- Copy MX and verification TXT from the dashboard. Paste only into the panel public NS actually name.
- Recreate named aliases. No shared catch-all across clients. HOLD unknown unless the retainer says otherwise.
- Lower TTL a day before the window if you still control the old MX.
- Cut to exclusive MailerZ MX. Delete leftovers. Query two public resolvers.
- Probe each public alias from an unrelated mailbox. File message IDs in the ticket.
- If send-as is in scope, upgrade and copy dashboard SMTP. Prove a unique subject from a third path.
- Keep the old mailbox login through old MX TTL plus a day as a drain store only.
- Export if counsel needs a file. Cancel the leftover seat. Write the close date before the window.
Failure modes and proof
Two MX brands in both resolvers is leftover MX. The ticket is not 'waiting on propagation.' Delete the other name.
Resolvers disagree on an exclusive set. That is cache. Wait the TTL. Do not add the old host back to 'help' the waiter.
Pretty zone on the wrong account is fiction. Confirm NS at the registrar before you edit Route 53, Cloudflare, or a reseller panel.
A green dashboard and an empty hop means the probe hit someone else. Parking MX and website-builder email products republish after a save. Re-query in the morning.
Client staff still sending from the old webmail after cut is a communications failure. It is not a reason to republish old MX.
Proof is timestamps, message IDs, resolver listings, and a cancel receipt. Mood is not proof.
MailerZ workflow and product boundary
Add the domain. Publish dashboard MX and TXT. Map aliases. HOLD or FORWARD unknown on purpose. Probe. Then send-as if the plan allows.
Boundary: not IMAP, not a campaign sender, not an open relay. Unhosted or unauthorized recipients get SMTP 550.
Envelope SRS only. If a bank later files a rewritten-From complaint, that complaint is about a different product. Do not rewrite Header From to 'look local.'
Store is fourteen days on Free and ninety on paid. That is recovery of hops MailerZ accepted. It is not an archive, not a legal hold, and not a backup of Gmail.
Agency plan is capacity. It does not buy dual MX, a dedicated IP promise, or an inboxing percentage. Do not write those into a statement of work.
Support owns product questions. Registrar lock and IAM live with the client or with you if the retainer says so. Split those jobs in writing.
Cost and alternatives
Workspace or Microsoft 365 per freelancer is the usual overbuy. If the client only needed hello@ in Gmail, seats were a tax. Quote forwarding against the suite invoice they already resent.
Cloudflare Email Routing is free inbound. It is not MailerZ leftover-MX stop, stored failed hops, or authenticated send-as. Fine for a brochure site. Thin for a retainer that includes proof.
ImprovMX and peers sit in the same class. Compare current limits, From handling, and logs. Do not paste a 2022 blog as a price.
Self-hosted mail is a second company. Agencies that promise it on a twelve-hour retainer will live in abuse queues. Only sell it if you already run it for yourself.
MailerZ Free proves the hop. Solo is forty dollars a year when one zone needs send-as. Starter, Business, and Agency step domains and aliases. Confirm /pricing the day you quote. Cards move.
The alternative that looks cheapest is leaving the old host. That alternative is leftover MX with a subscription. Price the cancel.
What to put in the retainer
Name the exclusive hop, the alias map, the catch-all policy, the drain clock, and the person who can change TXT. If those five lines are missing, you sold a vibe.
State that leftover MX is out of scope until deleted. State that self-send is not the acceptance test. State that MailerZ is not a suite and not a compliance badge.
Put a morning re-query on the runbook. Registrar website products republish MX. You will look sloppy if you close the ticket at 11 p.m. and a builder restores Google at 7 a.m.
Offboard is the inverse cut. When a client leaves, their new exclusive owner must exist before you drop MailerZ MX, or they accept bounce. Leaving both published is leftover MX with your hostname in it.
Filename exports with the zone and the date. Do not drop ten client PSTs into a folder named old mail.
If a second operator must run this without a call, the retainer should point at this page plus the migration planner. Config first. Exclusive cut. Drain without MX. Close on the TTL.
Fleet operations that keep retainers
One spreadsheet column per zone: NS host, MX exclusive date, alias count, destination, send-as yes or no, close date for the old seat. Slack memory is how Client B still has a 86400 TTL while you cancelled Client A.
Do not reuse prefixes across clients. support@ on two zones is fine. A shared Google Group that receives both is not.
Rotate the people who can open registrar email. Shared root users are findings. Agency work is least privilege plus a deputy for Sunday cuts.
Review HOLD queues on a calendar, not when a client screams. Free HOLD is a feature. An unread HOLD for a month is a neglected inbox with extra steps.
When you need more domains, upgrade. Do not invent a second MailerZ account per junior to dodge a plan. That splits proof and doubles leftover risk.
Custom domain email for agencies stays boring when every zone looks the same in the ticket. Boring is the product.
Google publishes how people evaluate helpful pages in Creating helpful, reliable, people-first content. Write the runbook for operators, not for a keyword.
Worked scenarios for agency buyers
A ten-client Webflow shop still has Google MX on four zones because a contractor enabled Workspace for Docs. The other six already sit on a forwarder. The buy is not 'migrate everyone this weekend.' It is a roster: Docs can stay; MX cannot stay dual. You quote four exclusive cuts, four drain clocks, and six leftover checks. Custom domain email for agencies fails when you sell one mood for ten different zones.
A franchise wants one hello@ on a parent domain and local aliases on twenty city domains. That is twenty-one exclusive MX sets, not one clever catch-all. Agency plan capacity matters here. Confirm the live domain cap on pricing before you promise the franchisee packet. A hidden second hop on a city zone is how one location 'never gets the coupons.'
A departing client asks you to keep receiving billing@ for ninety days 'as a courtesy.' That courtesy is leftover MX if you remain published, or a documented drain if you already cut them away. Write which. Courtesy without a clock becomes a year of their bank tokens in your HOLD.
A nonprofit board insists on Microsoft because a nephew works there. If they need Teams, buy Teams. If they need info@ in Gmail, do not buy twenty seats. The scenario is a conversation, not a fight. Put both prices on one page. Founders and boards pick the number they can explain.
An agency junior dual-publishes MailerZ and the old host 'during QA.' QA then passes because the junior probed the new hop. A donor hits the old hop. The postmortem is this page. Dual publish is not QA. QA is exclusive MX plus a third mailbox.
A white-label designer wants their MailerZ workspace hidden from the client. Hiding the hop does not hide leftover MX. If the client still has registrar email enabled, the designer will still get the ticket. White-label is branding. Exclusive MX is physics.
A sudden product launch adds eight role addresses on one zone. Free cannot do that. Starter or Business can. The scenario is an upgrade, not a second vendor beside the first. Two vendors is leftover MX with a press release.
Practice and anti-patterns for retainers
Practice: one spreadsheet column for exclusive date, one for old-seat cancel, one for who holds registrar 2FA. Anti-pattern: a Slack channel named email-stuff with screenshots from three years.
Practice: probe from a mailbox you do not own. Anti-pattern: the founder emails herself from Gmail and declares victory.
Practice: HOLD unknown per client. Anti-pattern: one agency inbox that receives every typo from every brand. That is a confidentiality bug you billed as a feature.
Practice: morning re-query after website builders. Anti-pattern: closing the ticket at 11 p.m. because the UI looked right.
Practice: write 'MailerZ is not SOC 2' in the proposal. Anti-pattern: a security appendix copied from a suite vendor.
Practice: offboard MX before you drop the retainer. Anti-pattern: cancelling MailerZ while you are still the published exchanger. Then you own a bounce with no contract.
Practice: filename exports with the zone. Anti-pattern: old-mail.zip on a laptop that leaves with a contractor.
These habits are how custom domain email for agencies stays boring. Boring retainers renew.
Operator closeout before you invoice the cut
Closeout is a dated packet: two resolver listings, probe message IDs, Header From screenshot, leftover MX absent, old-seat cancel owner, and the alias map the client signed.
If send-as was in scope, the packet includes a paid-plan line and a dashboard SMTP copy, not a remembered port. Free has no send-as. Do not invoice a 550 as a surprise.
If send-as was out of scope, the packet says so. Clients will still try to add the domain in Gmail. They will fail. That failure is documented, not a severity-one.
The drain clock is in the packet with the old MX TTL you actually read, not a folklore twenty-four hours. Plus a day. Then cancel.
The deputy is named. If you fly, someone can still disable an alias without guessing your password manager.
The next quarter review is scheduled. Plans and leftover products change. A closeout without a review date is a eulogy.
When the packet exists, you can invoice. When it does not, you are still in the window, even if the Slack emoji said done.
Edge cases agencies actually hit
IPv6-only networks that cannot reach an IPv4 MX hostname. Fix the host. Do not republish the old provider. History will show whether the new hop accepted the envelope.
A client whose NS still point at a dead reseller. You can edit Cloudflare all week. The world will not see it. Recover NS first. Custom domain email for agencies is downstream of delegation.
A country that blocks your destination Gmail. Forwarding cannot create a path the destination refuses. Say that before the cut. Offer a different destination, not dual MX.
A religious organization that cannot disable a volunteer-run Google Group that still owns MX. The volunteer is leftover MX with a ministry. Get the password or do not take the job.
Two agencies on one client, both 'handling email.' Demand one exclusive owner. Split-brain retainers are how leftover MX gets a second invoice.
A client on Agency capacity who still wants a catch-all FORWARD into your shared mailbox. Refuse. Capacity is not tenancy.
A merger that suddenly adds forty zones. Do not dual-publish during the merger PR. Cut in waves with clocks. Mergers already have enough coin flips.
Field notes from retainers that survived
The retainers that renew are the ones where email is boring. Boring means every client zone has the same ticket shape: NS host, exclusive date, alias map, destination, send-as yes or no, old-seat cancel owner. When a junior can open Client 7 and run the cut without a call, you sold custom domain email for agencies as an operation, not as a vibe. When only you can do it, you sold a hero, and heroes get sick.
Clients will ask for dual MX during a launch week. They have heard that DNS is scary. Your job is to say leftover MX is scarier. Offer a drain store and a clock. Offer a rollback that is one exclusive screenshot, not both names. If they still demand both, write the coin flip into the ticket and make them sign it. Most will stop asking.
Website builders are the quiet enemy. A designer publishes a new page and the builder's email product writes MX again. You closed a perfect cut on Thursday. Monday a donor hits the builder. Put the morning re-query in the retainer so you can bill the re-delete instead of apologizing for physics.
Shared agency inboxes that receive every client typo feel efficient until a journalist asks why you have another brand's donor mail. Named aliases and per-zone HOLD are how you sleep. Capacity on the Agency plan is not tenancy. Do not confuse a higher domain cap with permission to mix tenants.
Security questionnaires will ask for SOC 2. The honest line is no. MailerZ publishes controls on the security page and does not wear a badge. Agencies that paste a suite vendor's appendix into a forwarding proposal lose the deal later, when a reviewer can read. Lose it early or do not bid.
Offboard is where good agencies become leftover MX. You drop the retainer and remain the published exchanger, or you drop MailerZ MX before the client's new owner exists. Both are avoidable if the close date is in the roster before anyone is angry.
Quote live pricing the day you send the SOW. Free is one domain. Solo is forty dollars a year. Agency is the fleet card. Memory prices are how you eat a surprise upgrade.
If you need a second operator to understand this without you, send this page, the migration planner, and the leftover MX language on troubleshooting. Config. Exclusive cut. Drain without MX. Close on the TTL. That order is the field note.
Handoff memo for the next agency operator
Write one page a stranger can use on a Sunday. Registrar login location, DNS host if different, MailerZ workspace URL, alias list, catch-all policy, send-as identities, last successful probe IDs, and the client human who can approve a TXT change. Store it in the ticket system, not a personal drive.
Name the failure modes you already survived: a TXT pasted into hostname, a builder republish, a junior dual-publish. Future juniors will hit the same registrar UI. A memo without scars is a brochure.
Walk the new operator through one live change on a lab domain: add an alias, probe, delete the alias. Paper alone is not a handoff. The loop is.
Keep the memo format identical across clients so a hire can scan ten of them in an hour. Consistency is how custom domain email for agencies scales without you.
If legal and ops share one source of truth, link the memo from the retainer. If they do not, you will get two maps and one outage.
Acceptance criteria before you call the cut done
Two public resolvers show only MailerZ MX. A uniquely titled probe from an unrelated mailbox reached each public alias. Header From was intact. Hop history is non-empty. Unknown recipients followed the written HOLD or reject path.
The old host no longer accepts the domain. You checked from a network that is not the office VPN. Local resolvers lie.
The packet is in the ticket: timestamps, message IDs, dashboard screenshot, cancel owner, review date. Early silence is not success. Late complaints are.
If send-as was sold, a unique subject left through dashboard SMTP on a paid plan. If it was not sold, the ticket says inbound only.
Self-send was not the gate. Night CTA and start-free belong at the end of the client conversation, not in the first status email.
FAQ
What is the safest way to handle custom domain email for agencies?
One exclusive MX set per client zone, named aliases, a written destination map, and leftover MX deleted the hour you cut. Keep the old mailbox only as a drain store. Do not share one catch-all across clients.
Does this require a new mailbox for every client?
No. MailerZ is not IMAP. Keep the client on Gmail or Outlook unless they need a suite for Docs or calendar. Buy hosting only when they asked for folders on the domain.
Will it work with Gmail or Outlook?
Yes as destinations. Self-send is not proof. Probe from a third mailbox. Free has no send-as. Solo starts send-as at forty dollars a year. Confirm pricing.
What DNS records are involved?
Public NS that name the live panel, exclusive MailerZ MX, verification TXT, then SPF DKIM DMARC only if that zone sends. Leftover Google or Microsoft MX is a hard stop. See RFC 5321 and RFC 1035.
What should you test before a client goes live?
A uniquely titled probe to each public alias from an unrelated provider, hop history on MailerZ, Header From intact, and a morning re-query after registrar saves. Do not dual-publish to test.
When is MailerZ the wrong buy for an agency?
When the client needs IMAP folders, shared mailboxes, or a compliance badge you cannot honestly claim. MailerZ is not SOC 2, ISO, or HIPAA. Point those buyers at a suite and keep MailerZ off the proposal.
Key takeaways
- Custom domain email for agencies is one exclusive hop per client zone.
- Named aliases beat a shared catch-all across the roster.
- Leftover MX is a hard stop, not a rollback plan.
- Free is one domain. Agency is the fleet card. Confirm /pricing.
- Keep Gmail or Outlook unless the client asked for IMAP.
- Probe from a third mailbox. Self-send lies.
- Envelope SRS only. Header From stays intact.
- No SOC 2, ISO, HIPAA, or inboxing SLA in the proposal.
Conclusion and next action
Buy custom domain email for agencies as exclusive MX, named aliases, and a close date per zone. Do not buy dual providers as insurance. MailerZ can hold unknown mail and send-as on paid plans. It cannot merge leftover Google MX you left published for comfort. Start free on one domain, prove the hop, then scale the roster.
Ready to run client domains on one hop
Start free on a lab domain, then quote the fleet against live limits.
Inbound on Free. Agency when the roster needs more domains. Sign in if the workspace already exists.
Review quarterly, or sooner if provider behavior, pricing, or MailerZ scope changes. Author: MailerZ editorial, Secuno LLC.