There are a number of client protocols offered by Exchange Online to allow email clients to send email from their mailboxes. One of the most widespread protocols is SMTP Authenticated Submission (als...
Updated Aug 30, 2024
Version 3.0
Blog Post
@ Dame Hitting this throttling using multiple email clients will be extremely rare. Regarding messages created offline and queued for sending, an email client with a large queue of messages should only be opening a single connection to us and submitting the messages one by one. Clients would receive a temporary error and it should retry by itself without little for the user to notice. Outlook clients should not be affected by this as they should not be using SMTP Auth protocol to connect to Office 365 when there are more modern protocols available. This change will not have an option to opt-out. The connections from mobile phones or desktops will only apply when emails are actually being sent.
@Infiltrator There is no wait time of any significance. If you are not sending at the same time, you have nothing to worry about.