Is your client showing the actual "From:" header, or is it a broken one which is perhaps showing the SMTP MAIL FROM (the envelope sender) field incorrectly instead?

For instance, typically on a mailing list one will find a message arrives with the original "From:" header intact, showing the original sending person's address. But the SMTP envelope MAIL FROM field will have been changed to the list bounce handler address, e.g. an automated majordomo, LISTSERV, etc. server address. That way, the original sender isn't bombarded by all the bounced errors, because they only go to the envelope sender field, not to the "From:" header.

Only MTA's (Sendmail etc. servers) are supposed to use the SMTP envelope MAIL FROM address at all, and they are only supposed to use it to send "bounces" e.g. non-delivery error notices and other DSN's (Disposition Status Notifications).

But a number of broken mail systems over the years have incorrectly used the SMTP envelope MAIL FROM field instead of the actual "From:" header content, like most of the old "LAN" mail systems (Microsoft Mail, QuickMail, etc.) where there was a "gateway" to and from real Internet SMTP mail and it had a more limited set of headers and fields, on the internal LAN side, than the rich Internet mail body + envelope model.