Create crisp png file from text

I've lost count of the number of hours I've spent trying to find an answer to this, so help would be greatly appreciated...

I am very much at the beginning of learning how to use Ai, but thought the following exercise would be a good way of learning what I thought was a basic skill, whilst at the same time providing me with something that I need.

I have designed several simple logos for clients, most of which are based on text.

I would like to save the text as jpg and png files for use in websites and mass emails.

I am unable to do this without the files being blurry...

Here is an example of what I've done:  create text box in Ai, type in text font size 48 - export to png.  This png still looks blurry when I use it as an image in a MailChimp email.

There are other things which also seem to go wrong, but just knowing how to create a png or jpg file from a text box that stays sharp, would be such a relief, and so helpful.

Would someone be able to send instructions?