On 4/28/21 6:59 PM, Asai wrote: > Thank you, Wietse: >> >> This means that client systems are compromised with malware >> that sends email directly to the outside world, bypassing >> your mail server. >> >> To stop these, block outbound port 25 on your firewall for all >> systems except your mail server. >> >> Wietse > > Is it safe to assume that all legitimate email services, like Outlook.com for > example, are going to be using a submission service and not sending directly > over port 25, and that blocking port 25 on outgoing connections will not > interfere with normal email delivery?
Many legitimate ISPs (and even some cloud providers) block port 25 outbound, so yes. Demi
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