Suddenly unable to upload emails

[#1]

My wife's emails suddenly (no settings changes at this end) stopped uploading to her Ipad Mail inbox although she can send mail. I tested this on another Ipad which had the same result. This has been going on for sometime with Greenby who do not seem to be able to provide a solution apart from re-inputting the settings - this hasn't worked. She can  however access webmail. Yesterday the same thing started happening to me for my emails on 2 seperate windows 11 laptops. Bizarely I cannot upload any my emails except for the Greenby 'support' mails which upload perfectly well! I also can access webmail.

Any ideas on this

[#2]

1) Using the www.greenby.com web portal are all of your email accounts listed ?

Login to the Greenby portal with the same credentials as for the Plusnet Members Centre

2) Do the VIEW WEBMAIL buttons work for all of the accounts ?

3) Are you an "Email only" Plusnet customer ( like us ) where the free period is about 30 days ?

4) What errors are being displayed when your iPads fail to collect and fail to send email ? ( the exact wording please )

5) Make sure the Username is the full email address of the mail box for the POP3 or IMAP + SMTP servers 
avoid the older <account>+<name> format and I'd avoid using an alias too.

6) ISP & Mobile operators many block SMTP on Port 25, if you have Port 25 set change to 587 to avoid sending of emails being blocked.