For exchange accounts, we connect to the email servers via ActiveSync protocol which works over HTTPS. So we would only need access to port 443 with a valid SSL certificate to make the connection. 

If you have IMAP based email servers, then we would need SSL ports 993 for IMAP and 465 or 587 for SMTP.

You can narrow the range of IP ports to whitelist down to the 'us-west' IP block for AWS. Here is a resource where that IP range can be retrieved:

NYLAS US-WEST BLOCK IP RANGES TO WHITELIST:,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,

Please also whitelist our IP address is: and and as domains.

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