When you try to send emails from Outlook, you receive the following message:
An unknown error has occurred. Account: 'mail.domeniu.ro', Server: 'mail.domeniu.ro', Protocol: SMTP, Server Response: '451 Please try again later.', Port: 25, Secure(SSL): No, Server Error: 451, Error Number: 0x800CCC6A
This message appears when the IP you are logging on is in an antiSPAM blacklist. The problem is most common for ISPs that assign dynamic IPs (Clicknet, Vodafone, etc.); unfortunately this type of allocation allows one user's abuses to have repercussions on others in the same network (often entire classes of IPs belonging to these ISPs are introduced in anti SPAM blacklists).
To check if your IP is in a public anti-spam blacklist, go to http://mxtoolbox.com/blacklists.aspx and enter your IP in the form on this page. Click on the "Blacklist check" button and follow the "Status" column.
Solution:
- request the allocation of a static IP; then notify the Technical Department for entering this IP into an internal whitelist
- change your ISP
