From what you say, all 3 PCs are using the same e-mail service, because they have the same '@computers.com' address. Do you have any other PCs using the same e-mail address '@computers.com', which are not experiencing this problem?
If not, then the problem is likely to be at the server of the company hosting your e-mail.
I have e-mails hosted by several different companies and one in particular will start throwing the same error intermittently for a few days then it clears up.
I suggest you check with your e-mail provider. Are they experiencing load issues.