We have more than one client who is having the same issue.

They are on Spark connections (ADSL / Fibre) using spark provided equipment.
They have their mail hosted by third party cloud services ( all in NZ but different servers)
Mail is flakey with mail being delayed getting sent or mail not being allowed to sent. There are also issues with receiving, the mail failing to receive properly.
All their mail connnections are via SSL encrypted services.

Their connections are iMap / Exchange / Active Sync based. It is happening on more than one Pc in each client site.

When we take their broadband off the sprk router, put it onto our 3G based router (anothre  ISP) mail works perfectly. Put it back it fails.

The issue is intermittent but problematic enough that it is causing massive headaches.

Anyone else seeing this  type of behaviour?