Plusnet mobile not picking up plusnet email

[#1]

I am trying out a plusnet SIM in parallel with my Vodafone SIM (two handsets) with a view to switching to Plusnet.  On each phone I am using the android email client to hook up to my plusnet mailbox (via IMAP).  Each phone is set to sync email every 10 minutes.  WIFI is turned off so all the data is via the mobile network.  he phone with the vodafone SIM syncs every 10 minutes and picks up the new email.  but the phone with the plusnet SIM regularly fails to sync.  If I swap the SIM cards over, the problem follows the SIM.  Any ideas?

[#2]

Does the phone with PN SIM get other data - eg web browsing when it is on Mobile Data?

Was/is it a new number or have you ported a number to it?

[#3]

Hi. All data is via mobile and the web works perfectly. Just seems to be plusnet mailbox sync playing up. It is a new PN sim (new last December) no number ported. Has only started to play up the last week or two.

[#4]

Hmmm  sounds odd - did you see this on the Email forum?

https://community.plus.net/t5/Email/Plus-net-mail-on-mobile/td-p/1421502

[#5]

I hadn't seen that but my plusnet mailbox works with my android phones. But it doesn't always sync when used with a plusnet sim but it does with a vodafone sim (at the moment anyway).

I have noticed that mobile data with the plusnet sim is variable depending on which tower the phone hooks up to.

[#6]

Delete any Vodafone APN's and if it's an iPhone then delete the Vodafone settings folder.

[#7]

The only apns are orange internet, ee internet and orange mms.