Hopefully if you have this issue, you will find it helps you out.

I upgraded our office wireless access point to a Meraki MR12 recently. Immediately after doing so, my Evo 3D quit notifying me of new emails, both Exchange and Gmail ones. Our 3G/4G signal is weak in the office, so we use the Wi-Fi for both better data and battery life.

The problem occurs after the screen blanks and sits idle for 30-60 seconds. No new emails are being synced to the device. It isn't until you wake up the phone that they pull. The phone works fine on my home wi-fi and older office access point (802.11b/g)

Sprint CC could not answer the problem, other than that it must be our wi-fi connection. I went through the enevitable "factory wipe" of the device to no avail.

Only THEN did I stumble into the cause of it. There's an advanced settings menu in the Wi-Fi screens that I didn't know existed... Apparently it must only affect 802.11n connections. It is a check box labeled "Best Wi-Fi performance" Once I checked it, my emails started pulling when the phone was in standby.

Menu button

• Settings
  
• Wireless & networks
  
• Wi-Fi settings
  
• Menu button
  
• Advanced
  
• Check "Best Wi-Fi performance"
  

Anyway, maybe you all know it already, but wanted to pass on this tidbit of information.