Re: Question regarding smtp_per_record_deadlne parameter

[Viktor Dukhovni]

> On Dec 5, 2017, at 10:24 PM, J Doe  wrote:
> 
> That actually reminded me of something that crossed my mind, today - I forgot 
> about the inherently dynamic nature of routing.
> 
> Even though my server is within North America and it is extremely likely that 
> I am hitting the closest node of Google’s GMail servers in North America, as 
> routes are updated over time, there’s the possibility of the mail going over 
> a poor connection in a worst case scenario.
> 
> I know that’s less likely given the North American scenario, but it helped me 
> understand even more why this setting would not be enabled by default.

Note that distance alone would not typically cause any problems here,
the deadline time is applier per *line* from the client, whether an
SMTP command, or line of body content, and Postfix limits such lines
to 4096 bytes (storing partial lines in the queue file as needed to
support longer logical lines).

So to fail the deadline timer a sender would have to be unable to
deliver 4096 bytes in ~300s (no stress) or 10s (stress).  Either
way, that's enough time to stream 4k from the Moon at any plausible
bandwidth.  I don't think that deadline timers are nearly as risky
as one might conclude from the disclaimers, it is just that they have
not been as widely tested, so operational experience is limited.

-- 
Viktor.

Re: Question regarding smtp_per_record_deadlne parameter

[J Doe]

> On Dec 5, 2017, at 1:46 PM, Noel Jones  wrote:
> 
> If you're only connecting to google over a decent internet link, I
> doubt you'll see any effect whatsoever.  Kinda like me using polar
> bear bait in Tennessee.
> 
>  -- Noel Jones

Hi Noel,

That actually reminded me of something that crossed my mind, today - I forgot 
about the inherently dynamic nature of routing.

Even though my server is within North America and it is extremely likely that I 
am hitting the closest node of Google’s GMail servers in North America, as 
routes are updated over time, there’s the possibility of the mail going over a 
poor connection in a worst case scenario.

I know that’s less likely given the North American scenario, but it helped me 
understand even more why this setting would not be enabled by default.

- J

PS - Polar bear bait in Tennessee is actually very effective against the rare 
and elusive country music polar bear, a breed seldom seen but known to frequent 
those parts on vacation, in search of some tunes . . .

Re: Question regarding smtp_per_record_deadlne parameter

[Noel Jones]

On 12/5/2017 11:30 AM, J Doe wrote:
> Hi Noel and Wietse,
> 
> Thank you for your prompt feedback.
> 
> I think (in the quest to explore this more fully), I will try enabling this 
> for a short term and see what sort of TLS issues I may have.  The server I 
> described in previous mails is low volume so I believe it’s ideal for testing 
> something like this.
> 
> If anyone’s interested, I can always report back to the list about it.
> 
> - J

If you're only connecting to google over a decent internet link, I
doubt you'll see any effect whatsoever.  Kinda like me using polar
bear bait in Tennessee.



  -- Noel Jones

Re: Question regarding smtp_per_record_deadlne parameter

[J Doe]

Hi Noel and Wietse,

Thank you for your prompt feedback.

I think (in the quest to explore this more fully), I will try enabling this for 
a short term and see what sort of TLS issues I may have.  The server I 
described in previous mails is low volume so I believe it’s ideal for testing 
something like this.

If anyone’s interested, I can always report back to the list about it.

- J

> On Dec 4, 2017, at 7:39 PM, Wietse Venema  wrote:
> 
> Noel Jones:
>>> On 12/4/2017 3:35 PM, J Doe wrote:
>>> Hello,
>>> 
>>> I currently have a server that is configured as a mail forwarding domain 
>>> [1].  Using example.com as an example:
>>> 
>>>/etc/postfix/main.cf
>>>virtual_alias_domains = example.com
>>>virtual_alias_maps = hash:/etc/postfix/virtual
>>> 
>>>/etc/postfix/virtual
>>>u...@example.com users-gmail-addr...@gmail.com
>>> 
>>> As such, the SMTP client is used to forward the messages to each user?s 
>>> existing Gmail addresses.
>>> 
>>> I was reading more about the smtp client parameters and read about 
>>> smtp_per_record_deadline.  In postconf(5) it states that the time limits 
>>> are changed and that this ?...limits the impact from hostile peers that 
>>> trickle data one byte at a time?
>>> 
>>> Since my peer for the smtp client is always Gmail, this isn?t an issue for 
>>> me, but I was wondering - why does this default to ?no? ?  I note the 
>>> warning in postconf(5) that states for slow network connections this can 
>>> cause problems with TLS, but I am assuming that this doesn?t apply to most 
>>> configurations.  
>>> 
>>> Why wouldn?t I want this normally enabled ?
> 
> It's not safe to make this the Postfix default, but you're welcome
> to override that if you are sure that connections will never be
> slow.
> 
>Wietse