In short: sending email to mail.mydomain.net with postfix attempts a connection to fltr-2.mail.dreamhost.com and fails. I've tried to RTFM but failed to find why it redirects.
Details: I'm trying to get my Mac to send my dreamhost email.
I've got postfix configured as on http://wiki.dreamhost.com/Postfix#Configure_your_laptop.27s_Postfix_to_relay_your_email_to_Dreamhost_to_relay
relayhost = mail.lapin-bleu.net:submission
but upon sending email I get:
postfix/smtp: connect to fltr-in2.mail.dreamhost.com[188.8.131.52]: Operation timed out (port 587)
and indeed telnetting to fltr-in2 doesn't connect, while telnet mail.lapin-bleu.net 587 works.