The phrase "a regular letter" is correct and usable in written English.
It can be used to refer to a standard or typical letter, often in contrast to something more formal or informal.
Example: "Please write a regular letter to the company to express your concerns about the product."
Alternatives: "a standard letter" or "a typical letter".
A papal exhortation is an official statement issued by the Vatican that ranks below formal encyclicals, which are used to state the Church's position on things like abortion and contraception, but above a regular letter to the faithful.
Other than the means of delivery, an email is the same as a regular letter.
If you only have a regular letter size piece of paper, make it square by folding the left corner diagonally down to the right side.
Several annuals were printed; the first was announced in a September 1951 issue, in Morris's regular letter to his readers.
— Putting our regular letter carrier, Sam Park, in a headlock after Sam asked Blastich to sign for a registered letter.
Just because you're writing e-mail doesn't mean it shouldn't look like a regular love letter.
Online, the male skew of regular letter readers is even more pronounced (64 36).
She sat behind a small Lettera typewriter and a cardboard menu listing your options: you had to first chose your language (English or Spanish), type of letter (regular letter for $2, love letter for $3, illicit love letter for $5, postage included), and type of paper (blue, yellow, or onion).
Thatcher's rise to the leadership of the Conservative Party and the longest British premiership since the early nineteenth century, was reported in our pages via Mollie Panter-Downes's regular Letter from London.
Some evidence from the United States shows that regular letter based contacts with patients in the years after discharge may reduce the risk of suicide.
