I am not at all new to the AUR and I also had one comment that did not generate a notification mail on 2015-10-13 19:08 CET. Later comments (from this week) invoked notification mails, even on the same package. (I didn't have recent out of date notifications) So I guess there was a problem with the mail server or service but it is solved now.
I filed a bug report FS46742 [1] a couple of days ago about this exact problem since it affected me as well. However like already mentioned: It should be solved by now through a patch [2] by Lukas Fleischer (the main aurweb maintainer). The problem occurred due to a regression introduced in an earlier commit and was not a hardware/server problem. [1] https://bugs.archlinux.org/task/46742 [2] https://lists.archlinux.org/pipermail/aur-dev/2015-October/003818.h tml