Does CodeTwo Email Signatures 365 impact sending limits in Microsoft 365?

Problem:

You reached your daily sending limit while using a Microsoft 365 (Office 365) email account. Does using CodeTwo Email Signatures 365 cause mailbox to exceed the permitted number of messages faster?

Solution:

Microsoft 365 imposes a limit on the number of messages sent from a user mailbox per 24 hours. This is known as the Recipient rate limit and it is set to 10,000 recipients per day. If this limit is exceeded, messages can no longer be sent from the mailbox in question, as discussed in the following article on Microsoft’s page.

To enforce the limit, each user’s mailbox has a property in which the number of recipients is stored. Every time an email is sent from the mailbox, each recipient is counted towards the limit. When sending multiple messages to the same recipient, each recipient occurrence is counted separately.

The recipients are checked and counted in the user’s mailbox (Fig. 1., item 1). When working in cloud (server-side) signature mode, our software processes the message after it has left the mailbox and entered the Microsoft 365 submission queue, as shown in Fig. 1., item 2. At this point the recipients are already assigned by the user and our program does not add any additional recipients at any point. Furthermore, after receiving a signature in the CodeTwo cloud service, an email is transported to the Microsoft 365 delivery queue (Fig. 1., item 4), not to the user’s mailbox, so it is not possible that the recipients would be incorrectly counted again.

Fig. 1. Mail flow in Microsoft 365 with CodeTwo Email Signatures 365 - recipients are counted in step 1.

When working in Outlook (client-side) signature mode, our software adds the signature directly in Outlook (desktop, mobile & web / OWA). It does not affect the recipients of messages and the message flow in any way.