If I have a domain whose DNS is hosted by PN (and uses PN webspace), it is permissible (and will it work?) to insert new MX records with high priority (e.g. 0) such that all incoming mail to that domain is routed to another email provider? And if the sending email client uses TLS, will anything within PN’s environment block the connection (I can’t see why but …) ?
Zen from May 17. PN Business account from 2004 - 2017
If the domain currently has POP3 set in Email Settings on the Domain Names control panel I think any additional MX records you try to add will be ignored. Only if Other is set can you add these. However I think choosing that setting will immediately cancel association between the domain name and your account name so that trying to add back the existing MX record has no effect.
If you want mail routed elsewhere you should be able to select Other and add appropriate MX records but there will be a period where new emails are lost.
If you try to revert to POP3 I think you will need to get CS to refresh the email component on your account to restore proper server settings.