Use one – and only one – full stop or question mark at the end of a sentence.
Use a full stop, not a question mark, at the end of a reported question:
Use a full stop, not an exclamation mark, at the end of a reported command:
If a URL or email address is at the end of a sentence you can use a full stop – but never put it in bold unless the whole sentence is:
Never use a full stop if it will be followed or preceded by an ellipsis:
When it comes to exclamation marks, avoid them altogether. They look like you're shouting! Or angry! Or, as F Scott Fitzgerald said, like you're laughing at your own jokes. And they can trivialise your message.
Only use them if they're part of a book or film title:
Similarly, never use an interrobang (?! or !?)