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.