I can’t access my account
For help getting into your Gmail, use the Account access troubleshooter. If there is a chance your account has been compromised use the Gmail security checklist to secure it. For more help, see this Blog post.
Messages that have gone missing may be in your “All Mail” or “Trash” labels, or may have been accidentally filtered. Try going through this troubleshooting article to find your missing messages!
I’m receiving email intended for someone else
Just as with phone numbers, people sometimes type the wrong email address or are given the wrong one. However, if the other address has a different number of dots, that address is actually yours. In Gmail, homerjsimpson@gmail.com is the same as homer.j.simpson@gmail.com. You can learn more by viewing this help article or blog post.

Problems with the Gmail apps for Android or iOS