So I'm not able to send email on my phones using 4G on O2 or giffgaff, it works fine connected to my virgin wireless network, it's not just 1 phone, I have 2 on different sim cards, has the O2 network been blocked?
The meaning of the error VM305 means that the external IP address of the phone has been blacklisted, you can check this on your phone by going too https://www.spamhaus.org/query now the problem you are going too have is that the IP address is used by multiple users for the different providers that you use so removing it is going to problematic.
We know that if the device works across the wireless instead of using 4g then it isn't your devices that are triggering the spam, the best people to speak to would be giffgaff / O2 as it is their IP address that is on the spam list.
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