SQL & PL/SQL

Hello,

I have a pl/sql package that sends out emails using UTL_MAIL pkg poiting to an Exchange server. This package used to work fine for months but I recently noticed that some emails are not being sent as expected. The package loops through a set of action items satisfying some conditions and send emails based on that ( this number is expected to grow every day ). I checked the errors log and I found this error:

ORA-30678: too many open connections

I think this means that I have to close the connection everytime I send en email, but UTL_MAIL does NOT have a function or a proc to close connections, right ?

I don't know what causes this error to happen, but I suspect that this started happening right after we re-pointed the UTL_MAIL pkg from a Lotus Notes server to an Exchange server.
I am also seeing this error:
ORA-29279: SMTP permanent error: 501 5.1.3 Invalid address

I know where this error comes from (usually a null email id in the FROM or TO field ), but can this be causing the first error to happen ?

Please advise if you got this error before, is it a bug in oracle 10g as I read in some blog ? or is the second error happening make the Exchange server refuse SMTP connections ???

Thanks,
Sam