The error – 503 valid RCPT command must precede DATA is quite common and often occurs because of Outlook’s default anti-spam system or because of a setting that requires checking the messages before sending a new one.
To check if the problem is due to Outlook, it is necessary to open the program in Safe Mode:
- Open Start
- Click Search
- Write “outlook.exe / safe” (without quotation marks and with space between .exe and / safe)
- Try sending a message
If the above method does not work, there are two ways to solve the problem.
The first method is faster but temporary. Using Pop Before SMTP (requires authentication before sending new messages) you can send new messages for 30 minutes. After the 30 minutes have expired, you will not be able to send new messages unless you log in again. This method is not recommended because it is not compatible with servers that require SMTP authentication.
The following method is permanent and is the recommended solution for us,
because you will be able to send new messages without
Other possible solutions:
- If you use a VPN program when sending your email, you may receive this error.
- Be sure the account’s mailbox is not full or has a exceeded quota.
- Sometimes this error may occur if there is a corrupted Outlook PST file.
- If you use a program such as Mail Washer, you should disable the “automatically check at intervals” option because this program may affect the sending of emails.
- If you use multiple email addresses, check that the settings are applied to each of them.