Check that the address is correct and look in Spam or Junk. If available, try your provider's webmail to distinguish an account problem from a device or mail-app problem. Keep the exact bounce or error message.
When asking for help, provide the affected business email address, approximate send time and time zone, the mail app or webmail used, and whether sending, receiving, or both are affected. Share only the relevant error details and remove unrelated private message content. Do not send your password or one-time code. Email providers and settings differ; use the settings supplied for your account rather than copying another mailbox's configuration.