When previewing an email it is correct. But when I’ve sent it,it’s coming up wrong and adding different characters in?

This isn't the kind of experience I want you to have when sending an email in QuickBooks Online, morris-motors-ho. 

I've checked here on our records and there's no reported case about this one. Let's open a private browser and then try sending an email. The private mode prevents the cache from being kept while a website is active, which may cause problems. Consequently, a suitable location to tackle unforeseen issues like these. The following is a list of the shortcut keys you can use to get to one:

• Ctrl+ Shift + N for Google Chrome
• Ctrl + Shift + P for Mozilla Firefox and Microsoft Edge
• Command + Shift + N for Safari

If it works fine, go back to your original browser and clear its cache to start fresh. Moreover, you can use another supported and up-to-date browser to narrow down the result.

You may want to read through these articles to learn about creating and customizing templates:

• Add, customise, or remove logos on sales forms.
• Learn how to personalize and add specific info to sales forms.

I want to make sure that this is fixed for you, so after you tried the instructions, let me know how you did. As soon as you respond to this post, I'll get back to you. Take care always.