If you set name servers in your domain registrar but have not added the domain in your hosting company, what is the DNS status of your domain? nslookup xxx.com Server:  UnKnown Address:  yy.yy.yy.yy *** UnKnown can’t find xxx.com: Server failed…

According to rfc2822, an email message is:    A message that is conformant with this standard is comprised of characters with values in the range 1 through 127 and interpreted as US-ASCII characters [ASCII].  For brevity, this document sometimes refers…

Even after you set up a SPF record and a DKIM record, your email may also be rejected or delivered to junk box if you did not set up a DMARC DNS record. How to add a DMARC record in…

Cyrus-imap is an error-prone program. To debug it, you need to edit /etc/imap.conf to add “debug:1″ and create a user directory in /var/log/imap/log/admin to log the protocol messages. You need to know the log sequences for successful cases: Sep 14…

openssl s_client -connect domainhostseotool.com:995 user admin@domainhostseotool.com pass yourpassword stat (show total messages and size of the messages) list (show each message on a new line, including message number and the size of the message) retr messagenumber (retrieve the content of…

You may be looking for VPNs that open outgoing port 25. The famous VPN providers won’t tell you on their homepage they have blocked outgoing port 25 for preventing from spamming. You may have to buy one VPN after another…

When I migrated my website from CentOS 6 to CentOS 7, I found the wordpress site stopped working. Only the homepage can be displayed, other internal pages of the website “are not found”. Even the homepage is not displayed properly…

PTR record(or pointer recored, or RDNS record) is a DNS record in a DNS zone file. It maps an ip address to a host name or a domain name. It is used by mail servers to fight spammers. It is…

How to set an environment variable in Linux? You must know how to set a variable in bash:

You can show its value using:

  However, the bash variable is not an environment variable. The different between ordinary…

I have been using CentOS on my VPS. Today I need to install CentOS 7 on my PC. The installation process was not smooth and I had to do it in text mode. The main task during the installation is…