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I am trying to send an email to a recipient with an email address starting with a hyphen/dash, e.g. -localpart@example.com
The recipient claims the mail address is correct.
mail.log shows:
postfix/smtpd[26055]: warning: Illegal address syntax from ...[...] in RCPT command: <-localpart@example.com>
I am using Postfix 2.11.3
Any idea how I can send emails to such an address?
You can configure Postfix to accept such addresses with option allow_min_user = yes.
The postconf documentation also explains why the default is to reject such addresses:
Allow a sender or recipient address to have `-' as the first character. By default, this is not allowed, to avoid accidents with software that passes email addresses via the command line. Such software would not be able to distinguish a malicious address from a bona fide command-line option. Although this can be prevented by inserting a "--" option terminator into the command line, this is difficult to enforce consistently and globally.
As of Postfix version 2.5, this feature is implemented by trivial-rewrite(8). With earlier versions this feature was implemented by qmgr(8) and was limited to recipient addresses only.
Apparently, postfix has a setting (allow_min_user) prohibiting you from sending mail to addresses starting with a hyphen due to security reasons:
allow_min_user (default: no) Allow a sender or recipient address to have `-' as the first character. By default, this is not allowed, to avoid accidents with software that passes email addresses via the command line...
More here: http://www.postfix.org/postconf.5.html#allow_min_user
