After upgrading Typo3 from 4.1.6 all the way to 4.5.10, mails sent through the default Typo3 mailforms were messed up because the charset was wrong. The charset of the page was ISO-8859-1 consistently everywhere, but the Typo3 mailform expected input to be in UTF-8 and sent the mails as UTF-8 although the browser sent the data encoded in ISO-8859-1.
After lots of things I tried, the following TypoScript fixed the problem. You simply put it into the TS of the Template.
Of course you can put another charset in there if you have a similar problem with another charset.
It took me so long to find this out as the Typo3 code editor did not know the setting and it was not documented anywhere I looked at.
Maybe this helps somebody…