URGENT: Cannot send emails

[ccanei]

Sorry, it wasn't a ISP block.
Now I am receiving some error messages, like this one:
----------------------
From: Mail Delivery System [mailto:MAILER-DAEMON@webmail.virtualizeja.com.br]
Sent: Wednesday, 6 de julho de 2016 14:56
To: dulcevilela@carvalhovilela.com.br
Subject: Delayed Mail (still being retried)

This is the mail system at host painel.virtualizeja.com.br.
#################################################################### THIS IS A WARNING ONLY. YOU DO NOT NEED TO RESEND YOUR MESSAGE. #
###################################################################

Your message could not be delivered for more than 4 hour(s).
It will be retried until it is 5 day(s) old.

For further assistance, please send mail to postmaster.

If you do so, please include this problem report. You can delete your own
text from the attached returned message.

The mail system
<d.helena.vilela@bol.com.br>: connect to mx3.bol.com.br[200.147.36.13]:25:
Connection refused
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Now my question is: Why am I receiving 'Connection refused' error message?