If you use outlook as a 3rd party application for your domain email, Outlook itself is very vulnerable to viruses that are usually sent via email attachments. If you use outlook for daily domain email, you must use an up to date antivirus and you must periodically scan computers and laptops to ensure there are no viruses or malware on these devices. If your outlook has been hit by error 503 Valid RCPT, you can follow these steps to resolve it.
1. Login first in your outlook. after that select the file menu on the top right
2. After that, select File > Account Settings
3. In the account settings menu, select Repair.
4. Select Manual setup or additonal server types then next
5. Pada menu POP anda IMAP account settings pilih More settings
5. In the Outgoing server menu you can see the following image.
This RCPT Valid Error 503 obstacle when sending an outgoing email, then a bounce back message appears as below.
Your message did not reach some or all of the intended recipients
Subject:
Sent:
The Following recipient(s) cannot be reached:
‘alamat@email’ on ‘date’
503 Valid RCPT command must precede DATA
If you have followed the steps we have provided, the above problem should be resolved. The problem is not with your email provider, hosting or control panel account. Rather from the third-party application you are using, namely Microsoft Outlook.