I think misconceptions around the use of port 25 abound and 587 isn't just an alternative, there are official designations.
The official port for a mail client to submit a message to a mail server is 587/tcp.
The official port for a mail server to contact another mail server to deliver messages is 25/tcp.
Both can negotiate on use of TLS encryption (or none) - RobertoS - yes port 25 too.
This meant ISPs could block outgoing and even inbound traffic to destination port 25 and email clients would still work, but a customer would need to contact the ISP before setting up their own mail server at home (and/or use SMTP relays hosted by the ISP themselves).
Related, in olden times visitors would turn up at your office with clients configured for port 25 and start asking for your local SMTP relay IP while on site. When you told them to just use the official ports (587 or historically 465) and change the SMTP settings back to the original mail provider it was a revelation for them that these settings could work from any sensible Internet connection. One such person had been maintaining up to a dozen separate settings, one for every place they visited.
I'm also uneasy about trying to keep using email provided by a former home ISP unless paying / some kind of contract as it feels like it could go away at any time.
But I've used email since long before Google or Facebook existed and once I registered my own .me.uk domain, mailboxes and aliases have always been inclusive of the domain package.
prlzx on iDNET: FTTC (VDSL) at ~40Mbps / 10Mbps
with IP4/6 (no v6? - not true Internet)
Edited by prlzx (Mon 24-Feb-20 00:20:19)