Sendmail. Copy letters to the email address of a third-party mail server.

[mrrc]

There is a corporate mail server corp.com
There are users, for example user.
Mail received by him must be copied during the employee's vacation to an external mail address, for example user@gmail.com
If through /etc/mail/aliases (user: user, user@gmail.com), the SFP of the domain of the original sender of the letter is violated, because in fact, the message is already sent on behalf of corp.com and the receiving server can reject the receipt of such a letter based on the DMARC settings of the original sending domain of the letter.
Do you need to replace the sender's address with the domain corp.com? But so that the recipient sees in his post From the original addressee.
How to copy letters to an external address correctly in this case?
Thank you.

 

[usdmatt]

One of the fundamental issues with SPF. We've had this numerous times where our own emails that have SPF enabled have come back because a recipient has had a forward set up but not rewritten the address.

I find it a bit messy, but the supposed "correct" solution to this is SRS (sender rewrite scheme). Basically you rewrite the sender address to one under a domain you have control of and has SPF records that allow sending from your server doing the forward. The new address has the original sender encoded so that an email returned to your server can be further returned to the original sender. The new address looks something like the following -

SRS0=XZdE=IN=senderdomain.com=sendername@your-domain.com

I use postsrsd to do this with postfix but I assume there are ports that can implement this with other SMTP server software.

 

[SirDice]

If I take time off from work I really take time off, they can stick their corporate mail (and phone) where the sun doesn't shine. That said, why not implement a web mail gateway? So everybody can check their mail from anywhere in the world.

 

[mrrc]

this is SRS (sender rewrite scheme)

Yes.
I read a similar thread you contributed to in 2019.
But there are no practical examples of implementations, for example, for Sendmail?
Alternatively, this is a mail collector in the web interface of the user profile of a third-party mail server. Which would request POP\IMAP for a corporate mailer and take messages from there.

That said, why not implement a web mail gateway?

The ability to externally view your corporate mail is needed by no more than 2-3% of the total number of users.