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>ISPs blocking SMTP is this actually still a thing? I know on our campus network they block SMTP on the wired network, but not on the wireless (for some boneheaded reason or another).



All sane residential ISPs block port 25 (SMTP) to prevent spam.

All sane mail providers offer SUBMISSION (same protocol as SMTP) on port 587, which is intentionally not blocked by ISPs.


I've been on ISPs that block SMTP ans SUBMISSION along with their main alternative ports because they had too much spam sent from their IPs in the past getting them added to spamhaus.

Of course, they only needed to block port 25, but alas they blocked them all.


Residental ISPs where? I've yet to see one here in EU O.o


RCS & RDS in Romania [1]. Telekom in Germany [2].

[1]: http://www.rcs-rds.ro/asistenta/protejeaza-ti-calculatorul?t... (in Romanian)

[2]: https://www.telekom.de/hilfe/festnetz-internet-tv/sicherheit... (in German)


Most residential ISPs in the US, at least. Certainly all of the big ones do (Comcast, Time Warner, AT&T, Verizon, etc); the FTC has actually specifically recommended that all US ISPs block outbound port 25 as a spam mitigation measure.




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