I might be asking Pegasus to do something that is not possible but I would like to send mail from Pegasus to the SMTP server at Yahoo (converted from Cox) but have it show to the recipient as having come from my preferred gmail account. I thought I could do this by marking the "Use an alternate email address for the envelope" option in the SMTP General settings.

The alternate email option is not marked in the image above but when I do turn it on and try to send an email with that option on, I get the following error.

20:22:13.367: --- 22 Oct 2024, 20:22:13.367 ---
20:22:13.367: Connect to 'smtp.mail.yahoo.com', timeout 30 seconds.
20:22:14.543: [] SSL/TLS session established
20:22:14.543: [] TLS_AES_256_GCM_SHA384, TLSv1.3, Kx=any, Au=any, Enc=AESGCM(256), Mac=AEAD
20:22:14.543: [*] Peer's certificate name is '/C=US/ST=New York/L=New York/O=Yahoo Holdings Inc./CN=smtp.mail.yahoo.com'.
20:22:14.560: >> 220 smtp.mail.yahoo.com ESMTP ready
20:22:14.560: << EHLO [192.168.0.200]
20:22:14.617: >> 250-hermes--production-gq1-5dd4b47f46-fhdpd Hello [192.168.0.200] [72.223.113.21])
20:22:14.617: >> 250-PIPELINING
20:22:14.617: >> 250-ENHANCEDSTATUSCODES
20:22:14.617: >> 250-8BITMIME
20:22:14.617: >> 250-SIZE 41697280
20:22:14.617: >> 250 AUTH PLAIN LOGIN XOAUTH2 OAUTHBEARER
20:22:14.632: << AUTH LOGIN
20:22:14.688: >> 334 ..............
20:22:14.688: << ..............................==
20:22:14.747: >> 334 ................
20:22:14.747: << ..............................==
20:22:15.678: >> 235 2.7.0 Authentication successful
20:22:15.678: << MAIL FROM:bhenry004@gmail.com SIZE=422
20:22:15.820: >> 550 Request failed; Mailbox unavailable

It appears to login successfully to my Cox (Yahoo) account but then comes up with the "Mailbox unavailable" error.

When I have the option set off, the mail is sent correctly but with my Cox email address as the sender.

Am I using this option incorrectly or is it even possible to do this in Pegasus?

I just tried that option and got the following failure (email id disguised).

Delivery has failed on the enclosed message for the following
reasons reported either by the mail delivery system on the mail
relay host or by the local TCP/IP transport module:

550 Request failed; Mailbox unavailable

Your original mail message follows:

X-PM-Identity: All_Mail
From: b...@cox.net
To: b...@rochester.rr.com
Date: Wed, 23 Oct 2024 05:42:43 -0700
MIME-Version: 1.0
Subject: test with new option
Reply-to: b...@gmail.com
Message-ID: 6718EF43.19159.414EF5B@b....cox.net
Priority: normal
X-mailer: Pegasus Mail for Windows (4.80.102
Content-type: text/plain; charset=US-ASCII
Content-transfer-encoding: 7BIT
Content-description: Mail message body

reply to field set to gmail

Unfortunately I don't think what you are trying to do is possible. I have tried the same thing with several different providers without success. I believe that the Yahoo SMTP server is checking that the "MAIL FROM:" address is one of theirs and "Mailbox unavailable" is the result of that failed check.

Michael's suggestion of using the "reply-to" address is about the best you can do. The "From:" in the message will still be your cox.net address. Any reply 'should' be to the "reply-to" address although I have not found this to be very reliable.

Something that helped me is that I added a signature to every message that contained the line "Please reply to this address: me@mydomain.com".

Thank you Brian. I was afraid that would be the answer. I also tried several different combinations without success. The only thing that seems to work is to keep all mail addresses within the Yahoo domain. As you can see above, the "Reply to" option did not work either. I'll try your suggestion of the signature instructions.

Thanks for the rapid response.

Bob