Why do some letters not reach mail.ru?

Question

Email

Mail.ru for some reason does not accept some letters,

02/22/16 18:07:03	SMTP-OU	D222AB35C31849719BFF2A55851A56D8.MAI	868	217.69.139.150	CONN		220 Mail.Ru ESMTP	0	19	webmaster
02/22/16 18:07:03	SMTP-OU	59E11875B515474BB921C864D5D57F53.MAI	760	217.69.139.150	CONN		220 Mail.Ru ESMTP	0	19	webmaster
02/22/16 18:07:04	SMTP-OU	D222AB35C31849719BFF2A55851A56D8.MAI	868	217.69.139.150	EHLO	EHLO mail.ineu.edu.kz	250-mx152.mail.ru ready to serve	23	81	webmaster
02/22/16 18:07:04	SMTP-OU	59E11875B515474BB921C864D5D57F53.MAI	760	217.69.139.150	EHLO	EHLO mail.ineu.edu.kz	250-mx37.mail.ru ready to serve	23	80	webmaster
02/22/16 18:07:04	SMTP-OU	59E11875B515474BB921C864D5D57F53.MAI	760	217.69.139.150	MAIL	MAIL FROM:<[email protected]> SIZE=420374	250 OK	47	8	webmaster
02/22/16 18:07:04	SMTP-OU	59E11875B515474BB921C864D5D57F53.MAI	760	217.69.139.150	RCPT	RCPT TO:<[email protected]>	250 OK	35	8	webmaster
02/22/16 18:07:04	SMTP-OU	59E11875B515474BB921C864D5D57F53.MAI	760	217.69.139.150	DATA	DATA	354 Go ahead	6	14	webmaster
02/22/16 18:07:05	SMTP-OU	D222AB35C31849719BFF2A55851A56D8.MAI	868	217.69.139.150	MAIL	MAIL FROM:<[email protected]> SIZE=6430171	550 Unroutable sender address	48	31	webmaster
02/22/16 18:07:05	SMTP-OU	D222AB35C31849719BFF2A55851A56D8.MAI	868	217.69.139.150	QUIT	QUIT	221 mx152.mail.ru closing connection	6	38	webmaster
02/22/16 18:07:09	SMTP-OU	59E11875B515474BB921C864D5D57F53.MAI	760	217.69.139.150	DATE	.	250 OK id=1aXpGf-00074B-0j	420383	28	webmaster
02/22/16 18:07:10	SMTP-OU	59E11875B515474BB921C864D5D57F53.MAI	760	217.69.139.150	QUIT	QUIT	221 mx37.mail.ru closing connection	6	37	webmaster

As can be seen from the log, one letter passed, the other did not. And so it happens in influxes, then everyone leaves normally, then 5-10 pieces return a day. I can't understand anything. PTR is.

Answer 1

Your DNS servers are set incorrectly. Servers are registered in the parent zone

ineu.edu.kz     nameserver = ns12.zoneedit.com
ineu.edu.kz     nameserver = ns14.zoneedit.com
ineu.edu.kz     nameserver = ns.ineu.edu.kz
ns.ineu.edu.kz  internet address = 88.204.202.46

on your DNS only

ineu.edu.kz     nameserver = ns.ineu.edu.kz
ns.ineu.edu.kz  internet address = 88.204.202.46

while the ns12.zoneedit.com / ns14.zoneedit.com servers know nothing about your domain:

>host ineu.edu.kz ns12.zoneedit.com
Using domain server:
Name: ns12.zoneedit.com
Address: 46.101.18.226#53
Aliases:

Therefore, name resolution in your domain passes with a probability of 1/3.
You need to contact the registrar edu.kz (or use your personal account, if any) and change the list of DNS servers with the registrar.