Is there a way of customizing the subject line that is sent by email when visitors click the "Contact Us" link?

It would be helpful if the subject could include the name of the community so that when I reply, the subject is not just "A user sent a message via the contact form"

You can make that say anything you like by editing that language string. The string you are looking for is mailsub__core_contact_form

Please, see the following guide on how to use the standard translations if you are unsure on how to do this

https://invisioncommunity.com/4guides/themes-and-customizations/languages-and-localization_326/translating-using-the-standard-editor-r120/

Marc, is there a way to force a carriage return line feed in the language string when editing string?  I have edited one of our response emails with a change in the default text, but when the email is received there is no formatting with EOL.  All the content is strung together in one long sentence.

I will move this to our community support area, as this would be outside the scope of support. However essentially the language string is simply replaced with whatever you enter.

Agreed that the language string is replaced.  The problem is the formatting doesn't accommodate and enter key.  I would like it to display according to how I format the text in the language editor.

If the string is parsed as HTML, you can just add <br> as a line-break. 

Thank you! the <br> tag worked like  charm.