Why does list mail come out of order or hours/days late or never appear at all? Why do my AOL members not get all the list mail or digests? Why does it take hours or days for list mail to get to my Hotmail or Yahoo email box ...?

Because AOL, MSN, Yahoo email, Hotmail, Earthlink, et al, are large email providers. They get literally tons of email and they have to watch their servers carefully because they can get overloaded. So they prioritize. They give private email priority over group or list mail.

Yahoogroups is the largest email list provider (pay or free) and they send out literally tons of mail. Large chunks of that mail go to the largest email providers like AOL, MSN, Yahoo email, Hotmail, Earthlink, etc. Since those large email providers give priority to private email, when their servers are busy, they will refuse connections with Yahoogroups.

In other words, Yahoogroups tries to connect to them but their incoming mail servers say no, try again later. So Yahoogroups holds the mail and waits, tries again later until the email provider (AOL, MSN, Yahoo email, etc) will accept the connection and receive the mail from Yahoogroups.

So that's why things come late and out of order. In addition, AOL has admitted that they trash some email from Yahoogroups when their servers are busy, so some Yahoogroups mail is lost and never delivered to AOL members.

This also applies to the confirmations sent by Yahoogroups to confirm your email address or your subscription or unsubscription requests as well as notices to listowners and moderators about pending posts or members. Sometimes these confirmations and notifications take hours or days to get to you or never show up at all.

If you really want to check things out, you can review the full headers of delayed messages. The Received: lines at the top of the headers are the most recent, the top one will be when your ISP or mail provider received it from Yahoogroups. The Received: lines before that one are transfers between internal Yahoogroups servers. So look at the time on the topmost Received line and compare it to the time on the Received line just below that. Adjust for time differences if necessary and if there's a big gap, it means Yahoogroups was trying to contact your ISP or mail provider and couldn't get thru, so they waited and tried again and again until they got thru.

In the case of AOL, it's also possible there's a delay after AOL received it and before they delivered it to the AOLer's mail box as AOL has admitted that they do sometimes accept mail from Yahoogroups and then hold it somewhere in their system until their servers are not so busy and then deliver it to the AOL member's mail box.

Sometimes an ISP or mail provider isn't reachable after hours or days or trying to send mail and then Yahoogroups considers it a soft bounce. Some Yahoogroups list owners that use Yahoo email have reported seeing a message in their bounce history (go to My Preferences and click on Bounce History) that says "Yahoo mail servers unreachable for too long". This means Yahoogroups tried to send mail to them for a long period and finally gave up. This may happen with any of the large ISPs or mail providers if they experience temporary server problems and have to severely curtail their incoming mail for a period of time until the servers are fixed and list mail like Yahoogroups is always the first thing they restrict.