Which of the following commands checks for valid users on an SMTP server?
Option 1 : RCPT
Option 2 : CHK
Option 3 : VRFY
Option 4 : EXPN
1. RCPT
The RCPT Commands you tell the mail server who the recipient of your message is by using the RCPT command. you’ll send quite one RCPT command for multiple recipients. The server will respond with a code of 250 to every command. The syntax for the RCPT is:
RCPT TO:
Only one recipient are often named per RCPT command. If the recipient isn’t known to the mail server, the response code are going to be 550. you would possibly also get a response code indicating that the recipient isn’t local to the server. If that’s the case, you’ll get one among two responses back from the server:
• 251 User not local; will forward to -This reply means the server will forward the message. the right mail address is returned in order that you’ll store it for future use.
• 551 User not local; please try -This reply means the server won’t forward the message. you would like to issue another RCPT command with the new address.
2. CHK
Windows features a handy feature called CHKDSK (Check Disk) that you simply can use to analyse disk drive errors and run repairs automatically. It are often a lifesaver for handling (non-physical) disk drive faults.
A glitchy or corrupted disk drive can create a flash of panic. The potential for lost files is heartbreaking, and disk drive failure is one among the highest reported computer faults.
We explain the way to run CHKDSK in Windows 10 or 8.1 within the steps below. Remember, CHKDSK won’t be of much help if you’re handling a physically damaged disk drive (eg after dropping your laptop), but it are often an excellent tool for correcting minor errors.
3. VRFY
The VRFY commands enables SMTP clients to send an invitation to an SMTP server to verify that mail for a selected user name resides on the server. The VRFY command is defined in RFC 821.
The server sends a response indicating whether the user is local or not, whether mail are going to be forwarded, and so on. A response of 250 indicates that the user name is local; a response of 251 indicates that the user name isn’t local, but the server can forward the message. The server response includes the mailbox name.
4. EXPN
EXPN asks the server for the membership of a list . Its parameter could also be an encoded address or an inventory name during a server-defined format. If the server accepts the request (required code 250), its response text shows each subscriber to the list , one per line, during a server-defined format.
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