utl_smtp issues

We have used utl_smtp for emailing for years. Now all of a sudden on some of our servers, mail is not being sent when we use utl_smtp. Nothing in the datbase has changed. mailx on the unix server works fine.

What does utl_smtp do under the cover to send mail? I am assuming it makes some OS calls to send mail? There was probably some OS/network change or something. However, it is easier to track down if someone can help me figure out what utl_smtp does under the covers.

it does not appear to use mailx since mailx still works.

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