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If I do not add a port after the SMTP server, what port does Windows 10 Mail use by default, 465, 587, or 25? I checked on all the options including "Require SSL for outgoing email".

William
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2 Answers2

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It will try connections based upon these 3 ports, and the one that succeeds is then setup.

The default SMTP port is 25, so if no port is specified, 25 is used. If you require SSL, port 25 cannot be used, so in that case there always is a port.

465 is Secure SMTP, but 587 can be both secure and non-secure and is often used by STARTTLS, whereas 465 is often used by SSL/TLS.

LPChip
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  • I find that allowing mine to do the 'maintain automatically' will break it. It really wants those number in manually. [I have no clue why.] – Tetsujin May 07 '20 at 10:41
  • @Tetsujin its most likely that somewhere along the way, port 25 is blocked, and so it wants a different port. It is also up to the mail provider to have things setup correctly. For example, it may allow connections on SSL over port 465 but not respond to login unless 587 and STARTTLS is used. – LPChip May 07 '20 at 10:42
  • I think 25 is blocked at their end as some kind of simple anti-spoof measure. It used to work. – Tetsujin May 07 '20 at 10:44
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    @Tetsujin Most ISP's block port 25 nowadays to ensure that spammers can't do a quick hit-and-run to send out email over the default smtp server for an ISP. – LPChip May 07 '20 at 10:45
  • @LPChip "If you require SSL, port 25 cannot be used, so in that case there always is a port." do you mean I must add a port? But I did not add a port and it does not complain about an error. The SMTP server opens both port 25 and port 465. Will it use port 25+STARTTLS? – William May 07 '20 at 11:02
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    Well, this is windows Mail. I'm pretty sure that if you don't do it, it will under the hood anyway. If you select insecure email, port 25 or 587 is used. If you select SSL, port 465 or 587 is used. The defaults are 25 and 465, and most SMTP servers will allow these without much problem even though Starttls is preferred over port 587, so its quite likely Microsoft Mail will say: oh, you don't specify a port, let me try port 587 with starttls. Oh, this works, yeah, we'll use this. It should end up somewhere in the config though. There always is a port, somewhere. – LPChip May 07 '20 at 11:20
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In Windows 10 Mail app you need to setup the SMTP port for both incoming and outgoing messages:

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The sync was resolved as soon as I setup :993 and :465 after the nameserver

Francesco Mantovani
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