As a result of turning my mobile data off (hit my monthly limit) I have made what I think is an interesting find, and I'm wondering if others have seen the same, or could replicate.

Samsung Omnia, running 7.5, with mobile data currently switched off

I turn my phone on in the morning, and it connects to my home wifi network.  I can successfully access my Exchange email via ActiveSync.  Mail server address is mail.domain.com, which resolves to the external-facing IP address of our Exchange Server.

Get to work, and my phone obviously disconnects from my home network, and connects successfully to the wifi at work.  It picks up the new IP address info, including the DNS server.  This DNS server supplies an internal address for mail.domain.com.

While I can successfully browse the internet, my mail no longer connects, reporting a connection error.  Monitoring our firewall, I can see that my phone is still trying to access the external IP address for mail.domain.com, which is failing (by design).

To resolve this, I have to restart the phone.  Once done, I can successfully access mail at work.  However, once at home, after disconnecting from work wifi, and reconnecting to home wifi, it appears to be still holding onto the internal IP address for mail.domain.com, which causes mail delivery to fail.  I have tried just turning the wifi off then on, but the only way to get mail again is a shutdown/restart.

I'm imaging that this has been happening the whole time I have had the phone, and the issue has been masked by the phone falling back to mobile data when it can't connect via wifi, which has obvious implications for my data usage.

Had a quick search, but can't find anything similar.