This article describes the daily sending limits imposed by email vendors for the following services
If you have a valid business case for sending that would exceed these limitations, please submit your request at SMTP Mail Relay Allow List (vt.edu).
Throttle | Exchange Online | Gmail |
---|---|---|
Recipient Limit1 | 500 | 500 |
Message Size Limit2 | 150 Mb | 35 Mb |
Recipient Rate Limit3 | 10,000/day | 10,000/day |
Message Rate Limit4 | 30/minute | 2,000/minute |
1Recipient Limit = The number of unique users sent to per email message. Within Exchange Online, Distribution Groups count as a single user. Exceeding the limit causes the entire message to be rejected with a bounce back non-delivery report (NDR) emailed to the sender.
2Message Size Limit = The Maximum size (including attachments) of an individual email message. Messages exceeding the size limit will be rejected with a bounce back NDR emailed to the sender.
3Recipient Rate Limit = The maximum number of unique users sent to in a 24-hour period. Exceeding the limit causes any messages above the limit to be rejected with a bounce back NDR emailed to the sender until the rate limit rolls over.
4Message Rate Limit = The maximum number of email messages the server will accept within one minute. Within Exchange, sending more emails than the limit has the surplus emails sitting in Outbox that drain over time. No rejections or bounce backs, just delayed deliveries.
Based on a 24-hour period.
Limit type | Limit |
---|---|
Messages per day |
2,000/day |
Messages auto-forwarded |
10,000 |
Auto-forward mail filters |
20 |
Recipients per message |
2,000 total per message |
Recipients per message sent via SMTP (by POP or IMAP users) |
100 |
Total recipients per day |
10,000 |
External recipients per day |
3,000 |
Unique recipients per day
|
3,000 |
Above are the hard-cap settings against a mailbox, but Exchange Online Protection (EOP) can and does place more strict limits on sending depending on various factors within its “intelligent scanning”. Google has a similar feature that can suspend accounts if they are deemed too "spammy" or otherwise suspicious. This can result in a restriction or suspension occurring before those hard-cap limits are reached. Repeated offenses will be escalated, if this happens you may be placed on the blocked senders list. To attempt to remove yourself from this list, submit a request to Restore Ability to Send Email in Exchange Online.
Bulk Email Sending Knowledge Base Article
Restore Ability to Send Email in Exchange Online (vt.edu)
Sending Email to Random Sample of VT Addresses
Reducing the spam score of an email message (vt.edu)
SMTP Mail Relay Allow List (vt.edu)