An alternative to the app: pull your domain mail into an existing Gmail account on the web.
RECEIVING
- Gmail > Settings > See all settings > Accounts and Import.
- Under "Check mail from other accounts", click Add a mail account.
- Enter your business address, then choose "Import emails from my other account (POP3)".
- Username: the full email address. Password as set.
- POP server: mail.yourdomain.com, port 995, with SSL ticked.
- Tick "Leave a copy of retrieved message on the server" if you also read mail elsewhere.
SENDING
- Same settings page, "Send mail as", Add another email address.
- Enter your name and business address, untick "Treat as an alias".
- SMTP server: mail.yourdomain.com, port 465, SSL, full address as username.
- Confirm the verification code Gmail sends.
THE TRADE-OFF
Gmail collects by POP3 on its own schedule, so mail can arrive with a delay of several minutes. For prompt delivery, set the mailbox up properly in a client using IMAP instead.