I have an email account email@example.com with mail.live.com .
I also have a Gmail account. I have set up the 'Send mail as' feature in Gmail to send mail as firstname.lastname@example.org, and this works correctly.
My question is, if I send an email from Gmail 'as' email@example.com, how does the recipient's server verify that Gmail was authorized to send mail for example.com?
I have some knowledge of SPF records, and I know that the SPF record for example.com says that only messages originating from hotmail.com servers are valid.
The message that Gmail sends out has the @gmail.com address in the Return-Path and Sender fields, and so the SPF check is done against gmail.com and not example.com.
I have tested this with the test service at verifier.port25.com and it passes.
SPF check: pass DomainKeys check: neutral DKIM check: pass Sender-ID check: pass SpamAssassin check: ham