The “From” or “reply to” address of a message might appear as being one thing, but this doesn’t mean that this is the actual sender address for the message and therefore, the correct one to white list.
Whitelisting (and blacklisting) on the system is based on what is known as the “envelope sender” address or domain, which is the real sender address or domain for a message, this is because anyone can specify practically anything they like for the “From” or “reply to” address in their email client or sending application so this is easily faked or forged.
The envelope sender address is easy to find in that it’s usually at the very top of the message.
Once again, while in many cases the “from” or “reply to” address will be the same as the actual envelope sender address, if some sort of automatic or bulk/mass email is involved the real sender address may be different so it’s a good idea to check this unless it’s a regular sender. Adverts and newsletters, in particular, use a “VERP” type return address, which is a long random string used for tracking purposes, which are almost never the same as the “from” or “reply to” address in the message.
