Typeface design is an art. Specific typefaces have had books, the plural is correct, written about them and there is many a lecture at art colleges based on a single typeface, perhaps just the relationship between one character and the rest.
Don’t worry, I won’t bore you on the subject, although it is one I find fascinating. However, if you have a moment to spare, pop into a bookshop or library and check out the gestation of Times New Roman, the reasoning of Johnson’s Underground Sans and the design of Univers, this last being extremely popular in the 1960s, and often seen as an essential in graphic design. Now, for reasons that are interesting but nothing to do with us, it is used infrequently.
A bit of clarification: a font is a specific size of typeface, or a bold or italic version. However, the words have become interchangeable, much to designers’ regret.
A lot of research has been put into finding out how people read. Strangely enough, most tend to recognise the ‘white space’ between and around the words rather than read each individual character. What this means for us is that text, to be easily read, should be in lower case, i.e. non-capitals.
It also means that long sections of type in capitals, or even with initial caps, is difficult to read. We all know what a potential customer will do when anything that requires effort is presented.
You can divide typefaces into two types, if you'll excuse the pun: serif and sans serif, the later often shortened to sans. A serif is a little finishing flash on the end of a stroke of a character. Times New Roman is serifed, Arial is sans serif.
For once there is a general rule in email marketing: it is best to avoid 'normal' serifed typefaces when it comes to the body text. This is down to resolution. Most serifs are rather fine and this delicacy can be 'lost' on most media that emails are read on. In fact, it can give rise to optical defects that can distract. There are some 'faces with bolder serifs but these are a risk. Headlines, on the other hand, are a different matter.
Using a sans serifed 'face for the body text and a serifed 'face for headlines assists a reader to, albeit unconsciously, differentiate between the two functions. If you, perhaps, used bold serifs for sub-headings, and italic for captions, then reading becomes simpler and speedier.
It can be useful to choose a specific set of typefaces for specific functions. This will allow a reader to click through from a marketing email to a landing page without any feeling of disorientation. They will feel at home immediately.
It is perhaps best if you do not pick a 'face that is distracting. Currently, clean, pure lines are in favour. Many companies commission their own and given the cost, it shows that this step, not one I’m advising for smaller firms, can be useful.
Be consistent in your use of typefaces and the reward will be memorable, and effective marketing emails.