What Outlook POP3 port numbers should be used when connected to a Starlink network? I can receive emails but cannot send.
Assuming you are using a BTMail email account it does not mater what network you are using. The settings are for the BT servers as per this link.
BT Email server settings | BT Help
If you are not presently a BT Broadband customer or paying for your email through a BT Premium email account your email account will be a BTMail basic email account and this can not be used with an email client such as Outlook.
Earlier today, I was using a hotel wifi and didn't have any problems sending emails.
I'm now elswhere and connected by wifi to a Starlink system and I can't send emails.
Any suggestions why this has happened?
It could be a problem with your device or with Outlook or with the Starlink system blocking your email provider.
Try using webmail by logging onto your email account using a web browser. That would rule in or out your Outlook being the problem.
If it still won't send try a different network such as a mobile phone network or another broadband network.
Webmail works when using Starlink.
Outlook works when using 4G.
If webmail works as far as BT is concerned your email is working. While BT do not prevent the use of email clients and offer the server details they do not support them in as much as they will not assist if they don't work.
Given that Outlook works on 4g and not on the Starlink network I would try downloading a different email client such as Thunderbird to see if that works and if it doesn't work it would appear that Starlink are blocking access to the BT servers.