Should we write ‘Mr’ or ‘Mr.’ when addressing a letter to a male recipient? The issue is not so intricate. It’s got to do with contractions and abbreviations.
Contractions and abbreviations are both widely used in English. Yet they are different.
English students are most familiar with negative verb forms, such as aren’t and isn’t. These are the contracted forms of ‘are not’ and ‘is not’.
Abbreviations instead are used when we report only the first syllable of a long word. For instance, when writing dates: 5 Oct. 2017. Another good example is the word approx. which stands for “approximately”.
So, when you write the first and the last letter of any word, that is considered a contraction and must not be followed by a dot. Whereas when writing an abbreviation, you have to put it.
In conclusion, Mr is correct, and Mr. is not.
Perhaps the subject is a bit trite, but as English actor Michael Caine says ‘Not a lot of people know about it’.