When I enter an email address in a cell, Calc automatically converts it to a mailto: link. I don’t want it to do that. How/where can I turn that off?
Uncheck Tools > AutoCorrect Options... > Options > URL Recognition. Afterwards, none of the URLs or mail directions will be converted to a link.
If you want to have the URL recognition on, there is also this way:
As long as the email address (or another recognisable link) is not part of an extended text you can escape recognition by entering a simple formula like ="My.Self@ourdomain.cosm" or even ="mailto:MySelf@ourdomain.universe".