Moving cold email off Microsoft 365, Outlook and Azure mailboxes
Microsoft now limits new tenants to 10% of their external sending quota, and trial tenants to 500 recipients a day shared by every inbox. Move cold email to SMTP mailboxes that tenant limits don't touch.
- $2.50 a mailboxWarmup and a sequencer included, from 12 mailboxes
- Send from day onePre-warmed SMTP mailboxes at $4 a month
- Keep your sequencerSync to Instantly and Smartlead by API key
MC1454397 · Exchange Online
A new tenant's external quota, by tenant age
New tenants get 10% of their external recipient quota on days 1 to 30, 25% on days 31 to 60 and the full quota from day 61.
- External recipients for a whole trial tenant, every inbox included
- 500 a day
- What 100 inboxes on a trial tenant get a day, warmup included
- ~5 per inbox
What Microsoft changed
Two Microsoft changes that hit cold email from Microsoft inboxes
New tenants send at 10%, then 25% of their quota. Trial tenants get 500 recipients a day. Password logins for SMTP go off by default in December.
Mid-September 2026
MC1454397 starts rolling out
New tenants: 10% of the quota for 30 days, 25% until day 60. Trial tenants: 500 a day
End of November 2026
Rollout complete
Every new, trial and education tenant is on the new quota; free Education licenses count for less
End of December 2026
SMTP Basic Auth off by default
In existing tenants; an admin can turn it back on. Tenants created after December don't have it. OAuth logins are not affected
Second half of 2027
Final removal date announced
For everyone still logging in to SMTP with a password
100 inboxes on one tenant
The quota is per tenant, so inboxes split it. Warmup and follow-ups count against it too.
Azure inboxes share one pool
"Azure inboxes" and "Azure mailboxes" are Exchange Online mailboxes in a Microsoft tenant, so the tenant rules above apply to them. Seller prices and what a tenant includes: what Azure inboxes are and what sellers charge.
SMTP Basic Auth: check how your tool logs in
Most sequencers, Instantly included, connect Microsoft inboxes through Microsoft sign-in (OAuth), which this change doesn't touch. It matters for tools or scripts that log in to the Microsoft mailboxes with a username and password over SMTP, often an app password.
Three checks before December
Your sequencer's mailbox settings. SMTP host, port and password means SMTP AUTH; signing in with a Microsoft account means OAuth.
The seller, if you bought the mailboxes. Ask who the tenant admin is and how the mailboxes are connected.
Tenant age. Under 60 days means reduced quota.
Microsoft made two changes in 2026 that hit Outlook cold email sent from Microsoft inboxes, including mailboxes sold as Azure inboxes. MC1454397, rolling out until the end of November, cuts a new Exchange Online tenant to 10% of its external recipient quota for 30 days and 25% until day 60, and a trial tenant to 500 external recipients a day. At the end of December 2026, SMTP Basic Authentication, the password login for SMTP, goes off by default in existing tenants; that matters only for tools that log in with a password, because most sequencers connect Microsoft inboxes through OAuth.
The external recipient quota belongs to the tenant: every mailbox in it draws from one pool, so twenty mailboxes in a recently opened tenant share 10% of one tenant's quota. Mailboxes connected to a sequencer by SMTP password depend on the login that goes off by default in December. Microsoft's stated reason is abuse protection; neither notice names cold email. The quota formula and worked examples are in MC1454397 and the new-tenant limits.
Bounce codes
550 5.7.233, 5.7.705, 5.1.8: what the bounce means
The code tells you whether to wait, fix one mailbox or call Microsoft.
| Code | What happened | Next step |
|---|---|---|
| 550 5.7.232Clears in 24 hours | A trial tenant spent its 500 external recipients for the day | Wait for the rolling 24 hours, or move volume off the trial |
| 550 5.7.233Clears in 24 hours | The tenant spent its external quota; every user is blocked | Wait for the window to roll; a new tenant stays at 10–25% until day 61 |
| 550 5.7.705 tenant has exceeded thresholdNeeds Microsoft Support | Too much spam or bulk mail; outbound stops tenant-wide | An admin fixes the cause, then Microsoft Support lifts the block |
| 550 5.7.708Needs Microsoft Support | Low-reputation sending IP, more likely on new and trial tenants | Microsoft Support can grant a trial tenant an IP exception |
| 550 5.1.8 Access denied, bad outbound senderOne mailbox | One mailbox went over sending limits or an outbound spam policy; it still receives mail | An admin secures and unblocks the account; the block usually lifts within an hour, at most 24 |
550 5.7.232
Clears in 24 hoursA trial tenant spent its 500 external recipients for the day
Next: Wait for the rolling 24 hours, or move volume off the trial
550 5.7.233
Clears in 24 hoursThe tenant spent its external quota; every user is blocked
Next: Wait for the window to roll; a new tenant stays at 10–25% until day 61
550 5.7.705 tenant has exceeded threshold
Needs Microsoft SupportToo much spam or bulk mail; outbound stops tenant-wide
Next: An admin fixes the cause, then Microsoft Support lifts the block
550 5.7.708
Needs Microsoft SupportLow-reputation sending IP, more likely on new and trial tenants
Next: Microsoft Support can grant a trial tenant an IP exception
550 5.1.8 Access denied, bad outbound sender
One mailboxOne mailbox went over sending limits or an outbound spam policy; it still receives mail
Next: An admin secures and unblocks the account; the block usually lifts within an hour, at most 24
If you searched for "microsoft 365 tenant suspended cold email", the bounce decides the next step: 5.7.232 and 5.7.233 clear on their own (how to fix 550 5.7.233), 5.7.705 needs Microsoft Support. 5.1.8 blocks one mailbox: admins get the "User restricted from sending email" alert, and restricted users appear on the Restricted entities page in the Microsoft Defender portal. More in Microsoft 365 sending limits.
A Microsoft 365 cold email suspension caused by the list or the copy follows you to any provider. Recipient-side refusals are a separate case: why Outlook blocks cold email.
SMTP mailboxes
What moving to SMTP mailboxes changes, and what it doesn't
SMTP for cold email here means standard SMTP/IMAP accounts on your domains, on our own cold email infrastructure. There is no tenant quota to grow into and no SMTP AUTH switch to lose.
No tenant quota to grow into
Each mailbox sends up to 25 cold emails a day after 14 days of warmup, ready within 24 hours of the order.
Keep your sequencer
Mailboxes sync to Instantly and Smartlead by API key; SMTP/IMAP logins work in any other tool.
Outlook still filters
Run placement tests on Google and Outlook seeds before you move all volume.
If your outreach runs on Microsoft 365 or Azure mailboxes and you are hitting 550 5.7.232, 5.7.233, 5.7.705 or 5.1.8, Outreach2day SMTP/IMAP mailboxes are one way out: $2.50 a mailbox a month from 12 mailboxes ($30), warmup and a sequencer included, ready within 24 hours and sending after 14 days of warmup. They are not Microsoft mailboxes, so Microsoft's tenant quotas and SMTP AUTH settings don't apply to them. Outlook still filters every message you send, and we measure placement rather than promise it.
Outlook and Gmail still decide where each message goes, and some filters may trust Microsoft's servers more than ours, so test placement before moving all volume. Our IPs carry their own reputation, and our acceptable-use terms apply. A domain with complaints keeps them on a new server.
Plan
A 14-day move off Microsoft 365
Microsoft mailboxes keep sending while the new ones warm up, so volume never drops to zero.
Day 0 List every tenant with its domains, age and connection type, and look up each domain's registrant.
Days 1–2 Buy new domains in your name or connect your own. Order mailboxes at up to 25 cold emails a mailbox a day, 5 per domain. They are ready within 24 hours and warm up, with 25 warmup emails a day to Outlook.
Days 1–14 Microsoft mailboxes keep sending within quota; the new ones only warm up.
Day 14 Move volume to the new mailboxes and let the Microsoft ones finish their follow-ups.
After that Domains from a Microsoft tenant can move in a second wave once they stop sending: point the nameservers to us (24 to 48 hours), create mailboxes, warm up for 14 days. The switch replaces Microsoft's MX and SPF records, so its mailboxes on that domain stop working. Microsoft doesn't require removing the domain from the tenant first; once no users or groups use it, remove it under Settings > Domains (Microsoft's guide).
If campaigns can't pause
A new mailbox needs up to 24 hours plus 14 days of warmup. If campaigns can't wait that long, pre-warmed SMTP mailboxes at $4 a mailbox a month arrive with warmup history and start at a low cold volume on day one. They come on generic domain and mailbox names, so treat them as a bridge while mailboxes on your own domains warm up.
Pricing
$2.50 per mailbox a month
One price per mailbox. Pick how many mailboxes you need, from 12, and pay for exactly that many.
× $2.50 / month
- Cold emails a month
- Cold emails a day
- Domains needed
550 cold emails per mailbox a month (25 a working day from day 14); domains at 5 mailboxes each.
Every mailbox includes
$0 add-ons
Sending
- Warmup
- Our own sequencer
- One inbox for all replies
Deliverability
- Mailbox analytics
- Automated SPF, DKIM and DMARC
- SSL domain masking
- Spam checker
Build and scale
- API and webhooks
- MCP server
- Workspaces for clients and teams
- Live support
Domains are bought separately in the app, or bring your own.
Hundreds or thousands of mailboxes
Enterprise support for large teams
A shared Slack channel and a dedicated account team, for companies running hundreds or thousands of mailboxes
Talk to usFit
When to stay on Microsoft 365, and when to move
Microsoft 365
Microsoft 365Stay on Microsoft 365 if
- You need Microsoft or Google mailboxes. We don't sell Microsoft 365 or Google Workspace mailboxes. If a client requires them, keep a small setup on separate domains at low volume.
- You need 1 to 5 mailboxes. Our minimum is 12. A provider without a minimum is cheaper.
- You want to test first. There is no trial.
- You need a white-label portal for agency clients. We don't have one.
- The tenant hit 5.7.705 because of what it sent. Moving the same list and copy moves the problem. Fix those first.
Outreach2day
Outreach2dayMove to Outreach2day if
- Your Microsoft tenants are new or on a trial and the shared quota caps your volume.
- You are hitting 550 5.7.232 or 5.7.233 on campaigns that used to send.
- Your tool logs in to Microsoft mailboxes with an SMTP password.
- You want up to 25 cold emails a mailbox a day, from 12 mailboxes at $2.50 each.
FAQ
Questions about leaving Microsoft 365
Is Microsoft banning cold email tenants?
Microsoft has not said so. It has published MC1454397 and the Basic Auth schedule; a tenant sending too much spam or bulk mail gets 5.7.705.
Is there an SMTP alternative to Microsoft 365 cold email that keeps my sequencer?
Yes. Our mailboxes sync to Instantly and Smartlead by API key, and the SMTP/IMAP logins work in any other tool.
Sources
- 1Microsoft 365 Message Center. MC1454397: Updates to Tenant External Recipient Rate Limit (TERRL) quotas for new, trial, and education tenants, published August 14, 2026, updated September 29, 2026
- 2Exchange Team Blog. Updated Exchange Online SMTP AUTH Basic Authentication deprecation timeline, January 27, 2026, updated January 29, 2026
- 3Microsoft Learn. Fix NDR error codes 550 5.7.703, 5.7.705, 5.7.708 and 5.7.750, October 2, 2026
- 4Microsoft Learn. Remove blocked users from the Restricted entities page, (550 5.1.8), August 24, 2026
Deliverability call
Talk to our deliverability team
Book a call with the people who run our mailbox infrastructure. We look at your current setup and tell you what to change. Running 1,000+ mailboxes? We also quote a volume price below every vendor list price in our comparisons, warmup and sending included.
- Review your domains, DNS records and current inbox placement
- Size the setup: domains, mailboxes per domain and daily volume per mailbox
- Plan warmup and the move from your current provider or sequencer
- 1,000+ mailboxes: a volume price per mailbox for your setup
Free call
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