Q:

Emails not arriving - DNS settings? 

I am helping out a friend's organization.  They have problems with emails randomly not arriving (especially to Gmail it seems).  My first thought was to check the DNS settings.  Is there anything here that could impede proper email delivery? 
ftp                A    149.210.230.250
localhost           A    127.0.0.1
mail                A    149.210.230.250
domain.nl.           A    149.210.230.250
pop                 A    149.210.230.250
smtp                A    149.210.230.250
www                 A    149.210.230.250
domain.nl.           NS   ns1.deziweb.com. 
domain.nl.           NS   ns2.deziweb.com. 
domain.nl.           MX   10 mail
domain.nl.           TXT  "v=spf1 a mx ip4:149.210.230.250 ~all"
localhost           AAAA ::1
At first glance it seems strange that they have both NS records pointing to a different domain together with A and MX records.  The package that runs the website and (web)mail is site-helper.com .  Thanks in advance for any insights! 

A:

Email works intermittently because of the multiple records set for the root domain name which causes a conflict.  There are two possible scenarios here:

Remove NS records, and leave MX records as mail.yourdomain.com (which in it turn will point to the IP address  149.210.230.250).  This way the settings should take effect within 30 minutes or so. 
Point your domain name to the DNS ns1.deziweb.com.  and ns1.deziweb.com. ( if you want to have your domain name hosted with them) and set up all these records, including MX, on the nameservers ns1.deziweb.com.  and ns1.deziweb.com. 
In this case you will need to wait 24-48 hours for the changes to take effect. 

Hope that helps!  Let me know if something is not clear.