email notification problem

We're having an issue where some of our email alerts are not being sent, while some are. An excerpt from the notificationlogs.txt file follows (I've masked some info). Some entries indicate "Sending Email Notification for " followed by a text display name (those mails go OK), while some indicate "Sending Email Notification for " followed by the device's IP address (those mails do not go). I don't know if that is signficant.

It does not appear to be an issue with the email notification profile, since some emails log OK to a user, but others do not go OK to the same user.

Andrew Williams

06:14:53:010 Notifications: Sending Email Notification for vrsnylws through 10.10.0.228 at port 25
06:14:53:057 Notifications: Mail sent to user_name5@company.com,. Subject : Critical - VRSNYLWS
06:14:53:057 Notifications: Email sent successfully
06:26:59:245 Notifications: Sending Email Notification for 10.10.0.40 through 10.10.0.228 at port 25
06:26:59:245 Notifications: Exception occurred while executing Send Email action. Please verify the settings for the same:java.lang.NullPointerException
06:27:07:088 Notifications: Sending Email Notification for 10.10.0.40 through xxx.xxx.xxx.xxx at port 25
06:27:07:088 Notifications: Exception occurred while executing Send Email action. Please verify the settings for the same:java.lang.NullPointerException
06:33:55:745 Notifications: Mail sent to user_name2@company.com,. Subject : Test mail
06:35:45:635 Notifications: Sending Email Notification for 10.10.0.40 through 10.10.0.228 at port 25
06:35:45:635 Notifications: Exception occurred while executing Send Email action. Please verify the settings for the same:java.lang.NullPointerException
06:35:50:323 Notifications: Sending Email Notification for 10.10.0.40 through xxx.xxx.xxx.xxx at port 25
06:35:50:323 Notifications: Exception occurred while executing Send Email action. Please verify the settings for the same:java.lang.NullPointerException
06:40:39:736 Notifications: Sending Email Notification for 10.10.0.40 through 10.10.0.228 at port 25
06:40:39:736 Notifications: Exception occurred while executing Send Email action. Please verify the settings for the same:java.lang.NullPointerException
06:40:42:814 Notifications: Sending Email Notification for 10.10.0.40 through xxx.xxx.xxx.xxx at port 25
06:40:42:814 Notifications: Exception occurred while executing Send Email action. Please verify the settings for the same:java.lang.NullPointerException
06:42:26:439 Notifications: Sending Email Notification for 10.10.0.40 through 10.10.0.228 at port 25
06:42:26:439 Notifications: Exception occurred while executing Send Email action. Please verify the settings for the same:java.lang.NullPointerException
06:42:31:392 Notifications: Sending Email Notification for 10.10.0.40 through xxx.xxx.xxx.xxx at port 25
06:42:31:392 Notifications: Exception occurred while executing Send Email action. Please verify the settings for the same:java.lang.NullPointerException
06:51:24:002 Notifications: Sending Email Notification for 10.10.0.40 through 10.10.0.228 at port 25
06:51:24:002 Notifications: Exception occurred while executing Send Email action. Please verify the settings for the same:java.lang.NullPointerException
06:51:31:642 Notifications: Sending Email Notification for 10.10.0.40 through xxx.xxx.xxx.xxx at port 25
06:51:31:642 Notifications: Exception occurred while executing Send Email action. Please verify the settings for the same:java.lang.NullPointerException
07:01:02:189 Notifications: Sending Email Notification for 10.10.0.40 through 10.10.0.228 at port 25
07:01:02:189 Notifications: Exception occurred while executing Send Email action. Please verify the settings for the same:java.lang.NullPointerException
07:01:02:361 Notifications: Sending Email Notification for 10.10.0.40 through xxx.xxx.xxx.xxx at port 25
07:01:02:361 Notifications: Exception occurred while executing Send Email action. Please verify the settings for the same:java.lang.NullPointerException
07:01:26:595 Notifications: Sending Email Notification for 10.10.0.40 through 10.10.0.228 at port 25
07:01:26:595 Notifications: Exception occurred while executing Send Email action. Please verify the settings for the same:java.lang.NullPointerException
07:01:26:705 Notifications: Sending Email Notification for 10.10.0.40 through xxx.xxx.xxx.xxx at port 25
07:01:26:705 Notifications: Exception occurred while executing Send Email action. Please verify the settings for the same:java.lang.NullPointerException
07:01:45:767 Notifications: Sending Email Notification for psc through xxx.xxx.xxx.xxx at port 25
07:01:50:470 Notifications: Mail sent to user_name1@company.com,. Subject : Attention - PSC.BCOMPLETE.COM
07:01:50:470 Notifications: Email sent successfully
07:01:50:502 Notifications: Sending Email Notification for psc through 10.10.0.228 at port 25
07:01:50:549 Notifications: Mail sent to user_name3@company.com,. Subject : Attention - PSC.BCOMPLETE.COM
07:01:50:549 Notifications: Email sent successfully