If my IP is blacklisted or blocked by a specific ISP, will 250ok alert us?
Blacklist can only monitor public sources of data. This means private ISP blocklists, such as Comcast, Yahoo!, AOL, etc. cannot be queried for you to be alerted; however, that is one thing the Inbox can (potentially) identify. For example, sending to the seedlist and seeing mail as ‘Missing’ at an ISP means you should check your log files. If mail failed, it would likely be due to a blocking issue. If mail was delivered (and your mailserver received a 250 Ok), there is the possibility the ISP deleted it before placing it into a mailbox (amongst other potential possibilities such as internal delivery delays, an error on our side, etc.).