After the update i can't send attachments on mail to GMAIL and others

I have son Wordpress sites on my ISPConfig server (latest update). Alle the sites has the BackWPUp plugin for backing up and omptimize the db.

Before the last ISPC update, all was working fine. But now, after the update, the sites can't send attachments email, and i cant' understand why.

For example, i have a job with two actions: backup, compress (.tgz) and send the db via email and send the respective log via email too. The email with the log is sent, but the one with the db not

This is my CentOS 6.4 maillog:

The email with the log is sent to [email protected] and works
The email with the db, set to [email protected] don't works

I've tried setting a different recipient address ([email protected]) for the db attached email, but the issues persists

The WP log:

Code:

[19-mag-2014 12:34:22] One backup file deleted
[19-mag-2014 12:34:22] 1. Try to send backup with email …
[19-mag-2014 12:34:22] Sending email to [email protected]…
[19-mag-2014 12:34:23] ERROR: Error while sending email!
[19-mag-2014 12:34:23] 2. Try to send backup with email …
[19-mag-2014 12:34:23] Sending email to [email protected]…
[19-mag-2014 12:34:23] ERROR: Error while sending email!
[19-mag-2014 12:34:23] 3. Try to send backup with email …
[19-mag-2014 12:34:23] Sending email to [email protected]…
[19-mag-2014 12:34:23] ERROR: Error while sending email!
[19-mag-2014 12:34:23] ERROR: Step aborted: too many attempts!
[19-mag-2014 12:34:23] One old log deleted
[19-mag-2014 12:34:23] ERROR: Job has ended with errors in 2 seconds. You must resolve the errors for correct execution.

I have a second server, with Ubuntu, that has not this issue and is working fine. Same WP versione, same ISPC version, same plugin, same job

 

Up!

Any ideas?

 

Update: using php_mail capabilites we get "could not instantiate mail"

Someone can help, please?