From address doesn't meet the authentication requirements defined for the sender

[#1]

Something is not clear / quite right here.

Plus.com / Force9 / FreeOnline email services on the Plusnet platform do not have a hard quota and do not stop receiving more email when the 1GB quota is full.  On the Greenby platform the 2GB quota is hard and when full new email will not be received.  No accounts on these brands have moved.

On the Plusnet platform all the other brands have a 250MB hard quota.

@Stanleh wrote:
So I am trying to check the inbox of a plusnet email it's plus.com variant …

If that statement was correct then something does not add up … and certainly for me directed away from a full mailbox being the cause here.

Further, deleted items folders are culled every week by PlusNET’s house keeping for the 3 brands above.

[#2]

Ok so their email is user@user.plus.com, they told me they normally get warning emails when their account is full but nothing this time.

However I deleted about 6 to 10 emails from their deleted folder and they were suddenly able to receive my incoming test emails, however none of the emails from the last 48 hours have arrived, are they lost for good?

The other strange thing is, I emptied the trash can last night but when I looked again this morning some of those emails were back in the trash as though they had not been permanently deleted.

If you want I can boot up my computer and check their web account to see how much space was used but I believe it was somewhere around 600mb (it was late and I was extremely tired last night so I don't remember for sure)

[#3]

So I just checked the folder size and it was roughly 470mb and I didn't delete more than 10mb last night, could it have been plusnet had an issue with their servers and it got fixed and it was just a coincidence that I had emptied the trash at roughly the same time.

She really wants to know if she can get back any emails sent in the last 48 hours, they are now getting new emails (they just got one about a parcel being delivered) but still nothing from the last 48 hours.

Again thanks for all the help so far mate

Edit

Ok I just spoke to Plusnet and they said because their account has two emails the file size limit is spread across both accounts, although I don't have access to his email, he was still able to receive emails so I am not sure that theory makes sense.