The IRS will not make first contact with you by telephone. Only scammers call.
The IRS does not use email. Only scammers use email.
The IRS generally does not knock on the door. They do not have the manpower.
What is an IRS Certified Letter?
The IRS sends letters. Plenty of letters. Some contain questions about your tax return. Send these to your tax preparer. Other letters are bills or reminders you owe them money. You can take care of these by paying what you owe or working out a deal to pay all or some of it over a period of time.
The most important letters are the ones sent certified. You have to sign for them because these are the ones that give you your rights, along with a time period to exercise them. If you do not accept the letter or pick it up at the Post Office, you will lose your rights. Some people get the letter and do not open it. This is not a good strategy.
Why are these certified letters important? The IRS would prefer not to send these, but the law says they must. They will give you the right to contest the amount of tax you owe or the right to a hearing with a Settlement Officer before the IRS starts taking your wages and bank accounts. Failure to timely respond means that the IRS can go forward with whatever plans they have for you. Believe me, you will not like those plans.
What do I do if I Receive an IRS Certified Letter?
Do not ignore the IRS. Take advantage of the rights Congress has given you. You will be surprised at what can be done if you get help early.