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Igor Cicimov grabbed a keyboard and wrote:
> On 11/04/2014 2:52 AM, "David Guntner" wrote:
>>
>> Chris Angelico grabbed a keyboard and wrote:
>>> CNAMEs are immensely helpful, but they do have their limitations, so
>>> be careful. You can't, for instance, have a CNAME on mydomain.org and
>>> then also have an MX record on mydomain.org - so you'll have trouble
>>> receiving mail (unless DDNS lets you set an MX on
>>> myhostname.someddns.com, which I'm not sure about). You also can't
>>> have an SOA record, or any other type of record, on something that's
>>> CNAMEd elsewhere. Also, pointing a CNAME at another CNAME, while
>>> technically legal (I think), is potentially problematic - you may
>>> start seeing glitchiness with some clients, timeouts, etc.
>>
>> Good points. Within this particular context, I'm not sure that a SOA
>> record is that important, but it's worth noting.
>>
>> You're right about the MX record. By standards, a MX record should
>> always point to an A record and not a CNAME. In practice, I'm not sure
>> it actually has an affect on anything. I'm pretty sure, however, that
>> if pointing the MX to the CNAME doesn't work (or is problematic), you
>> can always point the MX to myhostname.someddns.com (which *is* an A
>> record) and your mail for the domain will still go there. It's been so
>> long since I've had to do this that I can't remember if I did that or
>> just ignored the standard and pointed the MX at the CNAME anyway. :-)
>> But I do know that I had no problems getting mail sent to my domain and
>> Postfix handling it on the local Linux box.
>
> The danger in this case is not with receiving but with sending emails as
> some mail servers might mark you as spammer and blacklist you due to
> dynamic domain linking.
That's not a "danger" associated with doing the above, that's a "danger"
associated with trying to send mail from your dynamic IP address that
your ISP assigns you. The two are unrelated.
Since it's true that a LOT of places will reject mail coming from
consumer IP address space (as opposed to business customer IP address
space) within an ISP's range, sending mail from your machine can be
problematic at best. I've found that the best way of dealing with that
is to use the smart relay ability of Postfix (and I would assume other
MTAs as well) and set it up to relay all outgoing mail off of your
provider's mail server. That way, the mail coming from you to another
service will be coming from your providers mail server(s) and won't
block it simply on the grounds that the connection is coming from
consumer address space. YMMV, but I've found it works very well.
--Dave
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