Using Mail, I can send from accounts that do not send from ntlworld servers.
I would just make one other comment in addition to the password reset advice @Graham_A has offered.
If you have your Ntlworld email accounts set to use the old smtp.ntlworld.com and imap.ntlworld,com (or pop3.ntlworld.com) email servers you should update the server settings to use the virginmedia.com servers.
For sometime now, VM have been recommending that all their legacy email domains (Ntlworld.com, Blueyonder.co.uk and Virgin.net) should be using the Viginmedia,com servers in email clients such as Mail. Here's their advice as to the correct settings https://community.virginmedia.com/t5/Email/Email-settings-change
Out of interest, I have just checked Mail in Windows 11 and if you create an account in Mail for an Ntlworld email address it automatically uses the server settings as per that Email-settings-change post.
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