punctuation - Commas in sentences with "when"

Is the comma necessary in the sentence below?

When a printing is finished, printer sends events to server.

Answer

All punctuation rules depend on your style (or preference) and the manual that you (or your editor) use.

If you have an introductory phrase, clause, or words that come before the main clause, you are supposed to use the comma. The following rule from Purdue University Online Writing Lab seems to confirm this.

2. Use commas after introductory a) clauses, b) phrases, or c) words that come before the main clause.

a. Common starter words for introductory clauses that should be

followed by a comma include after, although, as, because, if, since,
when, while.

While I was eating, the cat scratched at the door.

Because her alarm clock was broken, she was late for class.

However, don't put a comma after the main clause when a dependent (subordinate) clause follows it (except for cases of extreme contrast).

As explained above, you should not place the comma when the clause order is reversed.

Printer sends events to server when a printing is finished.