Introduction

This article describes the daily sending limits imposed by email vendors for the following services

• Exchange Online - individual account
• Gmail - individual account

Hard-Cap Limitations

Exchange Online and Google Comparison

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. 

Additional Google Hard-Cap Limitations

Based on a 24-hour period.

Limit type	Limit
Messages per day	2,000/day
Messages auto-forwarded Messages automatically forwarded to another account, not included in the daily sending limit	10,000
Auto-forward mail filters Account filters that automatically forward mail	20
Recipients per message Addresses in the To, Cc, and Bcc fields of a single email*	2,000 total per message (maximum of 500 external recipients)
Recipients per message sent via SMTP (by POP or IMAP users) Addresses in the To, Cc, and Bcc fields of a single email. Includes email sent using smtp-relay.gmail.com or smtp.gmail.com*	100
Total recipients per day Email addresses (recipients) count each time a message is sent; 5 emails sent to 10 addresses count as 50 total recipients.*	10,000
External recipients per day Email addresses outside your primary domain, including domain aliases and alternate domains	3,000
Unique recipients per day Each email address (each unique recipient) counts only once per day: 5 emails sent to 10 different addresses count as 10 unique recipients* 5 emails sent to a single address count as 1 unique recipient*	3,000

Soft Limitations 

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.

Additional Information

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)

Exchange Online Protection

SMTP Mail Relay Allow List (vt.edu)