Business Email Sending Limits

Every mail platform limits how fast and how much you can send. Ours exist to protect the reputation of the servers your mail leaves from — one compromised account sending spam would otherwise get everyone's mail rejected by Gmail.

The standard limits

These apply per mailbox and are the defaults every customer starts on.

A higher tier exists for customers with a genuine, sustained need. It is not something you can switch on yourself — open a ticket, tell us what you are sending and why, and we will discuss it.

Two limits are counted differently, and this confuses people

This is the part worth understanding, because it explains results that otherwise look inconsistent.

• Sending through webmail counts recipients.
• Sending through a mail client (Outlook, Apple Mail, a script) counts messages.

So one webmail message addressed to 60 people counts as 60 against your hourly allowance. The same 60 people mailed individually from Outlook counts as 60 as well — but a single Outlook message to 60 recipients counts as one.

If you are close to a limit and getting inconsistent results, this is almost always why.

A separate limit on long connections

There is also a cap of 10 messages per connection. A mail client that opens one connection and pushes hundreds of messages down it will be stopped at the tenth, even if you are nowhere near your hourly allowance.

Normal mail clients reconnect on their own and you will never notice. It matters if you are sending from a script or an application — have it disconnect and reconnect periodically.

What a refusal looks like

Both limits refuse with a 452 code, but the wording differs. Read the message, not just the number:

• 452 ... Maximum number of messages per session exceeded — the per-connection cap. Reconnect.
• 452 ... Rate limit exceeded, try again later — the rate limit. Wait, then continue.

A 452 is a temporary refusal. A well-behaved mail client will hold the message and retry automatically; you usually do not need to do anything.

If you need to send to a large list

Please do not use Business Email for bulk mail or newsletters. It is not the wrong-sized product — it is the wrong product.

A mailbox is designed for correspondence. Marketing mail needs unsubscribe handling, bounce processing, list hygiene and reputation management that a mailbox does not provide. Sending a campaign from your mailbox risks your domain's reputation, which then affects your ordinary business correspondence — the mail you actually cannot afford to have filtered.

Use a mailing service for campaigns. If you do, remember to add it to your SPF record (see the DNS article) — you may only have one SPF record, so it must be combined rather than added separately.

Staying under the limits

• Use a group alias rather than typing thirty addresses. One message to all-staff@ is one message.
• Spread large sends across the day rather than firing them in one burst.
• If a limit is genuinely blocking legitimate business, talk to us. We would rather raise your tier than have you work around it.