Exchange Online (Office 365) and SMTP

Recommended SMTP Settings for Exchange Online

Server Address: smtp.office365.com
Port: 587
Authorisation: TLS (1.2)
Connection Timeout: 60000
Batch Emails per min: As above, 20-25

Bulk message sending limits

Microsoft Exchange Online has a limit of 30 messages per minute per organisation. See https://docs.microsoft.com/en-us/office365/servicedescriptions/exchange-online-service-description/exchange-online-limits#receiving-and-sending-limits.

This can cause issues when using SMTP mailing. Accredo batch mailing can be slowed down, and errors can occur if you are trying to sending more messages than the limit allows. Issues can also occur if other organisation members are sending mail via SMTP from Accredo or another application.

To reduce the chance of errors when using SMTP with Exchange Online, we recommend limiting the messages sent from Accredo to between 20 and 25 per minute. This can be set in Navigator > Setup > Company > Configuration > Mail Settings.

Alternatively, if you need to send large batches and the long time to complete will be an issue, you can try the following:

• Use the Exchange Online SMTP relay.
• Run batch mailouts as a scripted scheduled task for out of hours.
• Use a dedicated SMTP provider for mailouts. This requires delegation from the domain and further configuration of domain and Office 365 settings.
• Use Exchange for all mailing. Exchange does not have the same constraints as SMTP for sending. This will require up-to-date anti virus on the client machine, or Outlook will request permission to send each message in the batch. For RemoteApp or Remote Desktop setups, this will require an Office Volume License on the server.