It's important first to find out if you can send an email. If you can't send an email, you need to solve this problem. By solving this problem you'll most likely solve your problem with receiving emails.
If you can and the problem is only when receiving them try the following
Set up your mobile phone for email.
FIND "ACCESS POINT NAMES"
Tap Applications.
Tap Settings.
Tap Wireless and network.
Tap Mobile networks.
Tap Access Point Names.
If still not working other option is that the MAIL SERVER ISN'T ACCESSIBLE FROM Your MOBILE NETWORK in this case you should get in touch with the internet provider ( this is very uncommon so I bet its not the problem)
and in the end, you can also check your phone memory and clean it a bit as that can help
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