Knowledge Base

Does CodeTwo Email Signatures for Office 365 impact sending limits in Office 365?


I reached my daily sending limit while using an Office 365 email account. Does using CodeTwo Email Signatures for Office 365 cause my mailbox to exceed the permitted number of messages faster?


Microsoft Office 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.


CodeTwo Email Signatures for Office 365 does not affect the sending limits in any way, as it does not interact with the recipient counting mechanism.

The recipients are checked and counted in the user’s mailbox (Fig. 1., item 1). When working in server-side signature mode, our software processes the message after it has left the mailbox and entered the Office 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 Email Azure Service, the email is transported to the Office 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.

Mail flow in Office 365 with CodeTwo Email Signatures for Office 365.
Fig. 1. Mail flow in Office 365 with CodeTwo Email Signatures for Office 365. Recipients are counted in step 1.

When working in client-side signature mode, our software adds the signature directly in the user’s Outlook desktop app. It does not affect the recipients of messages and the message flow in any way.