MS Outlook 2007 SP3 having intermittent problem sending e-mail. 1&1 is the host, and the e-mail is the generic info@ catchall for the business. 3 computers are configured for that e-mail (2 Windows 7, 1 Windows 10). The Windows 10 replaced an a third Windows 7 which had the exact same problem for the last several months. The Windows 10 is new and has the same problem. The other old Windows 7 computers have never had the problem. All computers are running Outlook 2007 SP3. Currently they all have the same settings for SMTP. 1&1 gave me a different SMTP server to try, but no difference. Outlook is using a PST file, which I imported calendar and contacts from the computer that had the problem (W7). The fix is to close Outlook, and run CCleaner, and then reopen Outlook and it works every time. This was the same on the W7 problem PC.