Not what I wanted Muskrat but thank you for trying!
I found the solution in the meantime: 
warn "DSN not supported!" unless defined $smtpc->supports('DSN');

[download]
D'oh!

In reply to Re: Finding supported ESMTP Extensions with Net::SMTP by dub4u
in thread Finding supported ESMTP Extensions with Net::SMTP by dub4u

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