[mdlug] Fwd: I can't email to mdlug at mdlug.org

[Carl T. Miller]

Yes, I'd be glad to.

There was a time that the mdlug server was getting
hit hard with spam and penetration attempts.  Since
most of this was coming from ISPs for home networks
and apparently compromised servers, I began blocking
email connections from various subnets.  With time it
became obvious that many of these subnets would
be part of a larger network, so I took a two-fold
approach: specifically allow the known good addresses
and block the bad larger networks.

This may seem drastic, but I needed to do something
quickly.  Since then there have been a few times good
senders have been blocked.  As soon as I find out
about it I investigate what IP addresses are allowed
to send email for a given domain.  The easy case is
when a proper SPF record has been provided.  For
example, "host -t txt carltm.com" displays my policy:
"v=spf1 a mx ip4:76.242.102.73 ip4:68.66.205.172 -all"

When no SPF records are found, I ask the person to
send email to carl at carltm.com and use the headers
to find the blocked IP address, which I can then allow.

Just an update...I plan to rebuild the mdlug mail/web
server sometime later this year and will find a better
automated solution to deal with unwanted connections.

Any questions?

c


On 1/3/22 9:11 PM, Robert James Fulner wrote:
> Carl,
>
> Out of ccuriosity could you tell us what you did, why, and what you
> suspected the issue was just in case any of run into similar issues on mail
> servers we personally run?
>
> On Mon, Jan 3, 2022, 7:30 PM Carl T. Miller <carl at carltm.com> wrote:
>
>> I believe that Steve will be able to send email effective
>> immediately, although he didn't give me enough info
>> to say for sure.  I will send him and message to make
>> sure he is able.
>>
>> c
>>
>>
>> On 1/3/22 5:38 PM, Gib wrote:
>>> FYI
>>>
>>> ---------- Forwarded message ---------
>>> From: Steve Litt <slitt at troubleshooters.com>
>>> Date: Mon, Jan 3, 2022 at 2:02 AM
>>> Subject: I can't email to mdlug at mdlug.org  T
>>> To: Gib <gibmaxn at gmail.com>
>>>
>>>
>>> Hi Gib,
>>>
>>> I'm hoping you can help me or send me to somebody who can. For the last
>>> 3 months I've tried to invite the Metro Detroit LUG members to GoLUG
>>> meetings, which happen 7pm Eastern time the first Wednesday of the
>>> month. But every time I email mdlug at mdlug.org, I get messages like the
>>> following for a couple days:
>>>
>>> ====================================================================
>>> Your message has been received by deedee.futurequest.net but has been
>>> undeliverable to the following recipients for at least 1 days.
>>> The mail system will continue to attempt to deliver your message
>>> to these recipients for a total of 2 days.  You do not need to
>>> resend your message at this time.
>>>
>>> Recipient(s):
>>>           mdlug at mdlug.org
>>> ====================================================================
>>>
>>> It doesn't give a reason for undeliverability. On the third day it gives
>>> me a failure notice. Is there a better address for posting to MDLUG?
>>>
>>> Anyway, if you can post to MDLUG, you're all invited to GoLUG's meeting
>>> Wednesday night at 7pm Eastern time. Details are at the following URL:
>>>
>>> http://golug.info
>>>
>>> Thanks Gib,
>>>
>>> Steve
>>>
>>> Steve Litt
>>> Spring 2021 featured book: Troubleshooting Techniques of the Successful
>>> Technologist http://www.troubleshooters.com/techniques
>>> _______________________________________________
>>> mdlug mailing list
>>> mdlug at mdlug.org
>>> http://mdlug.org/mailman/listinfo/mdlug
>> _______________________________________________
>> mdlug mailing list
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