Regarding Linode and Mail - default is blocked by Linode:
Sending Email on Linode
In an effort to fight spam, Linode restricts outbound connections on ports 25, 465, and 587 on all Linodes for new accounts created after November 5th, 2019.
If you have a need to send mail from your Linode, we ask that you first configure (1) valid DNS A records and (2) rDNS records for any Linodes that you plan to use to send mail. Then, open a Support ticket from the Linode Manager – we’ll ask you to provide the name of the Linode(s) that will be used for mailing.
Once you’ve completed those steps and provided that information, our Support team will be happy to review your request.