No, you should generally not delete them from your account. The "open" count is based on a blank image that gets displayed when the subscriber opens your email. In some cases, the image does not get display yet they still received your email.
Some reasons why the "open" might not register:
- The subscriber has an email reader that does not display images
- The subscriber receives your email in plain text form
- It is also possible that a given subscriber will open some, but not all, of your emails.
What if I still want to remove them?
If you would like to email people who are recording opens, you could use segmenting to create a sub-list of subscribers who have opened one or more of your recent campaigns. You will want to create a rule like "Opened <campaign name> OR Opened <campaign name>" and go back as many campaigns as you like.
Alternatively, create the opposite segment for "Did Not Open <campaign name>" to generate a list of people who have not recorded opens or clicks. Then you could manually review them, or export the segment and remove them from your list.