This is not an error message, but we are listing it here because it confuses some people.

VPOP3 sends a 'Transmission Receipt' when a message is sent out, and it contains a header asking for the receipt. The default configuration is that it will send the transmission receipt if the sender asks for a read receipt.

You can change this by going to Settings → Header Processing → Receipts/Urgent Messages, go to the Receipts tab and edit the Transmission Receipt Header fields box. If you clear this box, then VPOP3 will never send a transmission receipt.

In Internet email, there is no such thing as a 'Read receipt'. Even though many email clients have the facility for one, this is just something which has 'happened' rather than being designed. This means that if you request a read receipt from your email client you cannot tell how the recipient will behave.

1. Some email clients will automatically send a read receipt when a message asking for one is read
2. Some email clients will always ignore a read receipt, so you will never know whether it has been read or not
3. Some email clients will ask the user whether to send a read receipt or not

Currently, most will not send a read receipt automatically, as that would help spammers know whether an email address is valid or not.

So, if you ask for a read receipt, all you can tell is that the message has been opened if you do receive a receipt. You cannot tell anything if you do not receive a receipt.

Because of this, many VPOP3 users asked if they could be told once the message had left VPOP3, as that, at least, lets them know the message has been sent out. That is what Transmission Receipts are for