Generally speaking, the socket errors are caused by the network reason or the frequently connecting so that the mails are screened by the server. When appear such error, there are no special ways to solve but waiting for retry and chect the network connection. As to a domain name, if the socket error frequently appears, you can add its domian name in Domain Settings. Suitably decrease the maximal connection time, the maximal continuous connection time, suitably increase the retry delay time and continuous connection delay time in that Domain Settings. This can help decrease the screened time and improve the sending sccuess rate.