If you are sending an email campaign, you must test your emails to ensure they look correct on all receiving email systems—especially if sending from some web-based email systems.
Formatting errors often come from copying text from Microsoft Word into gmail or similar web-based email systems and sending it). If you send a test email to yourself (if using gmail–>gmail) the formatting appears normal. The error most likely is occurring for users opening your emails with Outlook–which a lot of people are using. Other mass email systems often have the same problem.
How to fix bad formatting errors:
Copy content from Word to your email draft
Highlight all the content and click the button furthest to the right of the text bar located at the bottom of the email draft screen (looks like a Tx). This removes all formatting.
Delete extra spaces that usually come up, change font size—you usually want 14 pt because of the higher resolution monitors (or fix anything you deem as off)
Send the email. It will be received without formatting errors!
Example of spacing errors (the first shows what you thought you sent–the latter shows what was received):