I have a MacBook and use Mac Mail for emails. I have a plusnet webmail account. and have it set up on my Mac Mail. However not ALL of the mails in my inbox at webmail are showing on my Mac Mail. Some are but the automay-tic email sent from my online shop isn;t. It shows in webmail but has not downloaded to my MacMail. Any ideas?
First it is helpful to understand that there is no such things as "webmail emails". All emails are held on the email server to be accessed via whatever email interface or application you chose to use.
The webmail interface is an IMAP email application, much like MacMail - in other words they both look at the content of the same server.
Can you please confirm that the MacMail program has been configured as an IMAP email client to the Plusnet Server (server address should be imap.plus.net using port 993) - you will need to look at the server configuration details in MacMail.
Notably, you seem to suggest that it is ONLY those emails from your online shop - therefore another consideration is that something on your MacMail / MacBook set up is treating those emails as SPAM ... and therefore not downloading them. If Mac Mail has options to whitelist senders, make sure that your online shop's sending address has been whitelisted.