Validating outlooks existance
I've setup a co-exist environment with Exchange 2010 and Exchange 2016.
By entering the characters as shown, you prove that you're a human and not an automated program.
Outlook will occasionally prompt you to verify your account again, just to make sure you're still you and your account hasn't been compromised by spammers.
SMTP traffic and HTTPS is proxied from the new Exchange 2016 installation - and works fine for the 2010 users behind.Not all servers respond with a "does not exist" error for missing accounts, so this is not completely reliable.If the server is an proxy (and/or external secondary server) for a number of other servers it might not know which accounts are valid on the next hop so will give "250 OK" for anything, and some servers are set this way in to stop spammers trying to enumerate valid accounts.We have all been doing email address validation for a very long time to make sure that the email is correctly formatted.This is to avoid users entering wrongly formatted email address but still they can accidentally give us a wrong email address.