From your post, I can safely assume that your tamagotchi already has a job.
Therefore, that [!] mail was the second job offer.
You have several options:
1. You can choose to ignore it and just leave it in your mailbox (it will be gone some time soon)
2. Choose the mail and wait to retain your job (he will look angry because you didn't pick anything but there will be no negative effects)
3. Choose the mail and pick the same job to play your current job's game (but somehow it doesn't remove the mail icon) until #1 happens.
4. Choose the mail and pick another job for a career change.