There's no rule about it, but it would be a nice touch. If they don't like it, what are they going to do?
you stick it on an envelope before mailing it
The answer is an envelope. It contains a letter.
please type a resignation letter
Chop your dick off, then stick it in an envelope and send it to him, it will definitely get his attention.
An acceptance of resignation letter is one that an employer writes acknowledging the resignation of their employee. The letter confirms their last day of work and other final employment details.
Where you are forced by the authories to sign a resignation (a letter to say you are giving up your job) which will terminate your employment.
The word is "envelope" (which usually holds only one letter).
A resignation letter is a formal way to tell your employer that you are quitting your job. It explains why you have decided to quit and when your last day will be.
Turning in a letter of resignation means that one is terminating employment with one's current employer. The common length of time for notification of resignation is two weeks to the employer.
You should have an attorney make a Power of Attorney resignation letter. If there is no attorney, you will write up a letter expressing your desires and have it notarized.
The word its is a possessive form of the pronoun 'it', used as an attributive adjective.It is less awkward than saying 'Put the letter in the letter's envelope' or '... the envelope of the letter'.
A formal or causal letter is usually mailed in an envelope.