Question about logs

[efk]

What does it means in Error logs/General this Couldn't get mail server response codes? I see 3 weeks ago is recorded this activity in 1 situation with IP address recorded and in 3 more situations without IP recorded in log. Each from these 4 logs are related with Guest, not with users, in one where is recorded IP there is no connection with known members.

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Guest

link - with word emailq mentioned in 3 logs is without IP address
/index.php?PHPSESSID=f3n80h0gn40jg20g0ngjf083f0fn9ugb98fb&scheduled=mailq;ts=65461781417 
and index.php?scheduled=mailq;ts=948416416486161

and in another link without emailq mentioned in link is where IP was recorded - /index.php?topic=1793.0;prev_next=prev

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