I recently installed a greylisting filter to fight spam; but have just noticed that there was at least one email from legitimate mail sever which was never retried and never delivered. I confirmed with its sender and its seems that there never was a delivery error report on his side, too. So if you wrote to me and I did not reply in a timely manner, you might be hitting this (mail server configuration) issue as well. In that case, please contact me through Contacts page; messages sent through that page are guaranteed to pass, and your email will get auto-whitelisted on my reply. Sorry for incovenience.