Unable to send emails from the server.
In MailEnable > Servers > localhost > Services and Connectors > SMTP > Logs > Debug > SMTP-Debug-xxxx.log the following information can be found:
02/07/16 08:44:11 ME-I0018: [0BCF8603898D4D25B155B5AFF7FB0FA4.MAI] Outbound message from ([SMTP:firstname.lastname@example.org]) requeued as [FFEFCD05AA0A4CE9B2E74C7CAA6D8FE5.MAI] to the target domain [example.com]
02/07/16 08:44:11 ME-I0123: Domain [example.com] has MX list [mx1.domain.tld,mx2.domain.tld]
02/07/16 08:44:11 ME-I0026: [FFEFCD05AA0A4CE9B2E74C7CAA6D8FE5.MAI] Sending message
02/07/16 08:44:11 ME-IXXXX: [FFEFCD05AA0A4CE9B2E74C7CAA6D8FE5.MAI] DNS resolved to the following record: IP Address=203.0.113.2, Family=2, Type=1, Protocol=6
02/07/16 08:44:32 ME-E0038: [FFEFCD05AA0A4CE9B2E74C7CAA6D8FE5.MAI] Communications Error: Socket connection to mx1.domain,tld failed (error 10060). The host was either not contactable or it rejected your connection. Socket Family = 2; Host=203.0.113.2; Port=25
It's not possible to connect to any mail servers despite of the fact, that ports 25 and 587 are opened on firewall:
telnet mx1.domain.tld 25
Connecting To mx1.domain.tld ...Could not open connection to the host, on port 25: Connect failed
TCP ports 25 and 587 are blocked by ISP (Internet Service Provider).
Contact your ISP regarding the issue.
Information about ISP can be found at http://whois.urih.com/ .