@Katharina Bormann in my experience they don't like those official looking letters in the mail so make sure you do that and also have a cost associated with unresolved issues like trash in your lease. 

Mailing would help, but I'd recommend going door-to-door if you could. 

Another reason to send it by mail is in many cases you will be deducting damages from deposit.  

A simple phone call or e mail  Hey you sold my friends house they loved you would you come to our house and help us like you did them.My wife got one yesterday daughter of one of her clients.. she has a 600k house to sell and wants to buy a 750k house ..

They have an app, scan your mail, forward mail, and will even deposit checks (forward/mail to your bank).

Quote from @Deborah Wodell: Bought a property with what we thought had a side yard full of junk and then discovered it was actually a small neighboring lot with zoning and public nuisance fines.

If you are really planning growth to scale then mail in house.

If you buy junk then yes, you might only get 2-3 years (at best).

I am doing some direct mail marketing in IE, LA county, Riverside county and OC county. 

I asked why she didn't mail the payment and she said she did not want to pay the 49 cents for the stamp, had an annual bus pass and riding on the bus gave her time to read books about real estate investing.