Hmm, depends on the definition of 'works' maybe :) Your solution doesn't result in any error or so, but it doesn't really test if the SMTP server supports DSN!

Did you try $smtpc->command('supports', 'DSN') with two SMTP servers, one which supports DSN and one that doesn't? I believe your approach wouldn't catch SMTP servers that do not support DSN. I believe Net::Cmd::command() is used to send protocol-level commands to the remote server.

However, checking if DSN is supported doesn't need interaction with the remote server. Upon creation of a Net::SMTP object, the object sends EHLO to the remote server and the remote server responds with the supported ESMTP extensions, which Net::SMTP stores in $self->{net_smtp_esmtp}. When called, Net::SMTP::supports() queries this hash.

Now you probably ask yourself, if this guy knows so much about this stuff, then why did he get stuck with the trivial defined. I think there is a point in that question... LOL