Presumably not on the SMTP servers they were connecting to. There are millions of IPs with port 25 open, without them email wouldn't work, so I'm not sure what you mean

They probably mean that port 25 is blocked on consumer ISPs/residential IP blocks to prevent malware from running an smtpd on an infected home computer or router (which used to happen a lot), but on a higher level of course no one blocks SMTP.