I normally track my plusnet email on my mobile (Utility Warehouse SIM) through imap.plus.com, but this stopped working yesterday. On further inspection, it appears to be impossible to form any connection to any plus.net domain server from the UW virtual mobile network (APN data.uk) including https://www.plus.net.
On the other hand, the UW virtual network seems to have no problem making connections outside the plus.net domain, and there is no problem accessing plus.net over my plusdsl.net VDSL2 connection.
Strangely, it is possible to access www.plus.net over the UW virtual network using the Tor browser. Equally strangely, the plus.net servers can be accessed using the same UW SIM via the underlying EE network (APN everywhere).
I thought that the problem might be over zealous censorship of connections by the UW/EE/Symantec 'parental control' filters, so I asked UW to turn them off. As a result, I can now access adult content over the UW virtual mobile network, but plus.net remains inaccessible.
I am raising this here because the problem might be due to a firewall or other networking error at plus.net. Even if problem lies elsewhere, then investigating it from the plus.net end might prove fruitful.
Well... Whatever was wrong seems to have been resolved by someone, so all is good. If anyone out there understands enough about how APN configurations influence Internet access then I would be interested to understand what happened.