This is a question that conceivably spans subject spaces, but starting here because my first suspicion is an os configuration.
Oracle 11.2.0.4.0 Std. Ed. One, 64-bit
Oracle Linux 6
We have a procedure that runs periodically to check for blocked/blocking sessions in the database. If any are found, it calls a procedure that utilizes utl_smtp to send an email to the DBA group. The mail body is a clob containing XML output of the query that collects the information.
While we don't get many, the last couple that have come have been absent the mail body. In looking back through mail logs, I can determine the last 'good' email was on May 2 and the first 'bad' was on Oct 26. (That long between occurrences.) When it first happened I did some initial checking, but had to let go for other priorities. Now I'm able to take a closer look and have determined that no code changes occurred during that time, for either procedure. What DID change was that we migrated from Oracle Linux 5 to Oracle Linux 6, which leads me to wonder if something might be different about the mail function/configuration at the OS level. That's way out of my area of knowledge, so don't know where to begin looking.