Sending newsletters
Sending limits and pacing
Last updated June 30, 2026
Because your newsletter sends from your own Microsoft 365 mailbox, Microsoft’s per-mailbox service limits are the real ceiling on how fast a send can go out, separate from your plan’s monthly allowance.
The practical limits
As of this writing, Microsoft 365 mailbox limits are approximately:
- About 10,000 recipients per day per mailbox.
- About 30 messages per minute per mailbox.
- Up to 500 recipients per single message.
Exact numbers depend on your Microsoft 365 plan and Microsoft’s current service limits, so treat these as guidance and confirm against your tenant.
How pacing works
SimpleNewsletter365 sends one recipient at a time and spreads large sends over time so you stay within your mailbox’s limits rather than tripping them. A limit on concurrent active newsletters per mailbox prevents one mailbox from being overloaded.
Monthly allowance vs daily limit
Your plan’s monthly send allowance is not a daily burst limit. A large monthly allowance still sends within the daily mailbox ceiling. High-volume senders can connect more than one Microsoft 365 mailbox to send a large volume in a tighter window.