Using Mailer/sendmail.pm version 2.06:
By default the -t flag is set when sending mail via sendmail and
Mail::Mailer. There should be an option to turn this off, as there is
always a chance that you don't want mail sent to the address in the
email that has been composed. For example, I am using it to send out
list messages. These are received, processed, and retain their original
To: field (the mailing list address), but I certainly wouldn't want it
delivered back there!
I have edited sendmail.pm and removed the flag, but I thought I should
highlight this issue.
Another point worth noting is that versions of Postfix since 2.1 allow
the -t flag to be set as well as a list of email addresses on the
command line (going against the comments in the same code).
Thanks.