MX Record Change Propagation

Everyone says 24-48 hours I think to cover their butts but I changed a MX Record 6 days ago and a customer is still getting email (almost all spam) to the old MTA. As mentioned 99% of what is still coming to the old MTA is spam but why in the world, after 6 days, hasn't everyone picked up the change? and I have a feeling they will still be receiving mail to the old MTA for quite some time.....
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Mal OsborneAlpha GeekCommented:
Spammers tend not to send email very well. They often don't check DNS frequently, and usually do not retry failed sends. They also may have queued these messages up somewhere weeks ago.

In theory, DNS servers should look a the SOA EXPIRE record for your domain, this tells them how long entries should be cached for.  It is a good idea to lower this before you start making DNS changes, if it is set to 1209600, (two weeks), then lower it to 86400 (24 hours) a few weeks before making changes. It can be reset to a higher value again once you have finished changing stuff.

Some ISPs ignore this, and cache DNS records for longer than they should, to save bandwidth.  

I would not worry too much about spam, just wait until your changes are older than the SOA EXPIRE, and you should be good.

If you don't know your SOA EXPIRE value, post the domain name here and someone can look it up for you.

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LockDown32OwnerAuthor Commented:
Well... the domain is and from what I can tell the SOA is 1 week. So give that to me in layman terms again. Other DNS servers will let cached entries stay for 1 week? Since I an getting emails from all over that would mean that several DNS servers are letting DNS entries be cached for a week? Isn't there some kind of RFC that dictates how long?

I have no control over the SOA. They use and I am not thrilled with them. I called support twice yesterday and asked then what the TTL was on the MX records and where on their web site I could see it. Both times I was told 1 hour and you can't see it anywhere. I think that is bull. Every place I could check says it is 24 hours. Can you see anything different?
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