Problems with email

[AndroidNewby]

I am with TalkTalk and it just doesn't work with the default Email app. (you get incoming mails, but sent mails go to the Outbox then the Sent mail folder, and have a 'Sent' tag, but they never arrive.) So I changed to the MyMail app which impressively set up my account. It sends and receives emails (apparently OK). My problem is that I sometimes get an envelope icon on the 'top line' of the phone; I swipe down and it says something like you have two messages. I tap on the entry - and everything disappears. There's nothing in any of the MyMail folders, and nothing on my webmail. So I sent an email to MyMail asking for some help and explanation as to what is happening and seemed to get a reply (an envelope and an indication that it was a reply to my sent mail) but when I tapped on it it disappeared!
Can anyone suggest what's happening, please?
Note that my handle is AndroidNewbie - this is my first exposure to this operating system/smartphone
Thanks,
AndroidNewbie.

 

[neu smurph]

I'm with TalkTalk as-well and have the same problem with the stock Email app. I use K-9 Mail as an alternative which works perfectly.