The problem started this week on my work mail. I am able to receive incoming mails but cannot send any outgoing mails. At first, I thought it was a server issue of our host 1and1.com, but my other host, Technographx.com was also experiencing the same SMTP error.
After reading online and asking my brother, It seems that PLDT has blocked port 25 for outgoing emails. Try Using Port 587. My colleague also did this on his Globe Broadband connection in Cebu and is now able to send emails.
What’s more irritating is that these ISP’s didn’t even issue any notice to their subscribers about this. Are you also having trouble sending emails on your ISP?