You can use smtp port 587.
For example in MS Outlook in the advanced settings, change the outgoing port number from 25 to 587.
For MS Outlook:
Tools > Email Accounts > View or change existing account
select the email account and press Change button
Click on More Settings...
Click on Outgoing Server tab
keep (o) Use same settings as my incoming mail server
Click on Advanced tab
under Outgoing server (SMTP)
change 25 to 587 in front of it.
Press OK and save those settings.
If you get a warning about SSL certificate not being trusted, please
ignore that warning or ask the support to update the SSL cert for exim.
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