Before folding the letter, make sure that the address on the inside of the letter matches with the one that you have written or printed on the envelope.This will help avoid any mixups.
Don’t forget to check that you’ve signed the letter.
 Make sure that the text is facing up and towards you. This is your last chance to proofread and double check that you haven’t forgotten anything.For example, have you dated the letter? Are there any spelling or grammar mistakes?

, Take the bottom of the letter and fold it so that it is about half an inch (about 1 cm) from the top of the page.You can place the envelope underneath the letter to use as a guide. Make sure that when you have folded the letter up, it is small enough to fit inside the envelope.
 Make sure to line up all the outside edges of the paper before creasing so that you don’t end up with a crooked fold. If the fold is crooked, your letter may not fit into the envelope.Use a ruler to make the crease nice and sharp. You can do this by holding a ruler sideways and using the thin edge. Slide the edge of the ruler along the letter on the creases so they are nice and flat.
 You will now take the right part of the letter and fold it about one third of the way in.Line up the top and bottom edges of the letter and then crease the fold.
 Take the other side of the letter and fold it one third of the way in. This will be the same thing that you did with the right side.Line up the top and bottom of the edges so they are perfectly straight before creasing.
 The last crease you made should go into the bottom of the envelope first. Place it so that the folds face the backside of the envelope.This will make it easy for your recipient to find where to begin unfolding the letter.
Check the address.
Lay the letter on a table.
Fold the bottom half up.
Crease the fold.
Fold the right half of the letter inwards.
Fold the left half of the letter inwards.
Turn the letter sideways and insert into the envelope.
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