When choosing which fonts to use, it's important to make sure you're always following the licensing agreement. Some fonts found on free font websites are only free for personal use or by donation. Any usage not following the font license could result in costly legal action and fines.
VERIFY THE LICENSE
Read over your font license agreement before proceeding with any usage. This guarantees that you're covering all the bases before you start designing. Most fonts will have a web font license available, which means it's okay for email use. However, if you have materials to print, you may not be able to use the same font. Some fonts have a print-only license.
CHECK THE USAGE NUMBERS
If you only purchase a single-use license for a font, it's not valid to share on multiple computers or with your third-party design vendors. The license outlines how many computers the font can be installed on, as well as any online traffic restrictions for web fonts (you pay based on how many visitors you have on your website).
Some font libraries like Google Fonts, are free for personal or commercial use. These are a great alternative if you don't have a license for some of the larger type foundries.