Apple mail fails with Submission

[Adi Pircalabu]

On 2018-12-18 07:33, Ruud Voorjans wrote:
> Dear all,
> 
> I'm running dovecot # 2.3.2.1 - Pigeonhole version 0.5.2 () - OS:
> Linux 4.18.0-12-generic x86_64 Ubuntu 18.10 with Submission.
> It works great except with apple mail (Iphone).
> 
> I get an error with the MTA  (postfix):
> ""postfix/submission/smtpd[32552]: warning: non-SMTP command from
> mail.example.org [1][xx.xx.xx.xx]: Content-Transfer-Encoding: 7bit""
> 
> with other mail-client(s) (Outlook (Desktop and Iphone app)) i have no
> problem and it proxy-sends the e-mail beautiful out to the recipient.

Hardly anything to do with Dovecot. When it comes to email clients Apple 
Mail has been and is still one of the worst flops (no offence intended, 
just my opinion based on personal experience). If you can reliably 
reproduce it, try and log the raw SMTP conversation between Postfix and 
the client by enabling per IP debugging in Postfix:
postconf -e "debug_peer_level = 20"
postconf -e "debug_peer_list = xx.xx.xx.xx"
postfix reload
where xx.xx.xx.xx is the unlucky client IP address.

Possibly some crappy SMTP PIPELINING implementation at the Apple end, 
who knows.

-- 
Adi Pircalabu