A common question

When sending an email, the message header typically includes the “From” and “To” fields. Adding a recipient as “CC” simply extends the list, resulting in a single email delivered to all listed recipients.

However, when using “BCC” with, for example, 100 recipients, the sending server must generate 100 individual emails, as BCC information is not passed to downstream servers. This segmentation is appropriate, but it means each message may traverse a different route to its recipient, especially for bulk senders.

For instance, if 100 emails are sent from your GEN Services account, they may be processed by any of four different Message Transfer Agents (MTAs), each with its own configuration and IP address. This is standard practice.

If a sender has a poor reputation and utilises multiple servers, it is likely that one or more of these servers may be blacklisted, causing some messages to be delivered while others are rejected.

Large providers like Google operate hundreds of mail servers, many of which may be listed on spam blocklists. Their emails are distributed among these servers, with delivery ultimately occurring from a server that is not currently blacklisted, despite the provider’s substantial email volume.

This distribution across multiple servers explains why delivery from the same sender can be inconsistent; emails may arrive on different days or times, and some recipients may not receive a message that others do.