This gauge counts the total number of SMTP sessions that the identified SMTP ALG instance has inspected. It tells an administrator the overall volume of mail traffic passing through that particular mail-relay inspection point, which is the denominator needed to judge how significant the spam and drop counts are. For example, if this value reads 50,000 sessions checked, a spam count of 40,000 on the same ALG would indicate the mail server is under heavy spam bombardment rather than handling mostly legitimate mail.