In the android version, i get an lart a new email has arrived, but when clicking on open on the front screen, it is not yet in the android app. it takes several minutes from the emclient alert unil ican see the mail in the app
If the email takes along time to open / display after you press the notification and the app is already running in the background, that usually means the Mail client “is still busy synching” and / or “is not fully locally cached yet” so delays opening the new message till that’s all completed. That can happen if you have only recently just added your accounts.
if you don’t have the Mail client already open in the background but it’s fully synced and fully cached locally, then when you press the new mail notification, “the app then has to first load” and “then the new message will open” so can be a slight delay. On my own mob that’s aprox 2-5 secs.
You can see if it’s still synching your accounts after opening the app, via pressing “Menu / Settings “ at the top left. Then press “Show Operations”. So if you have only just recently added your accounts it can take time to locally sync depending on the size of your server mailbox and your acct d/l settings.
If you have an eg: IMAP, Exchange / Office 365 type account, you can speed up message opening / reading on new mail notifications by going to “Menu / Settings” and then “Open your account.
Then under “Services” press on your account eg: IMAP and you will see “Sync Options” where under that you will see “Customize download options” to set either Message List, Full Messages without attachments, or Full Messages with attachments.