It is possible to send e-mails successfully from my neoCatalog but in fact the e-mails do not arrive.
There are times that the error is returned by the e-mail server after a few seconds (10-20 aprox.) so neoCatalog has already shown the message that everything has gone well before the error actually arrives.
To solve this problem it is necessary to activate the SMTPS. Go to Administration > Preferences > E-mail Server Settings and tick the "User SMTPS" option.