Full stops are used:
 To mark the end of a sentence:
And then you put it in the mail, and you repeat this process ad infinitum until the damn thing sells.
 To mark the end of a group of words that is not a full sentence, but which is complete in itself:
Over and over. Again and again. Relentlessly.
 After abbreviations that consists of the first part of a word:
Sept. Thurs.
 In email and website addresses:
www.oup.com.
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