Firstly, make sure to check your spam folder. If a Teamer message is in there, make sure to flag it as not spam. For example, in Gmail, you can drag your message to the primary inbox to let them know Teamer emails are safe. Teamer has taken all the necessary steps to ensure a high delivery rate, but flagging Teamer messages as safe is the best solution.
Do you or your players have smartphones?
If so, downloading and using mobile apps will fix both issues. The app uses push notifications which always get sent regardless and can't be filtered.