Re: [Jmap] Address Validation (was Re: Submission)

[Paul Smith <[e-mail]>]

On 24/04/2017 22:37, Adrien de Croy wrote:
>
>>
>> On all the mail systems I know, if you try to send mail at a domain 
>> that doesn't exist, it fails instantly.
> I've seen a lot delayed, especially when the initial submission server 
> forwards to another pre-configured "smarthost" which then delays it 
> further. 

I've seen delays as well. Often related to badly behaved DNS servers 
which do strange things with non-existent domains (eg not returning 
anything, rather than returning an NX error). The mail server then 
should play safe and retry for a while.

Remember that a lot of mail servers are deployed on small networks with 
badly behaving infrastructure. Eg - how is a mail server supposed to 
indicate whether a recipient address is valid if the Internet connection 
is down and the DNS server has crashed? I know it seems unpopular here, 
but there are good reasons for a lot (not all) of the ways things happen 
with SMTP/IMAP4.