Black list
Blacklists are lists of IP addresses, domains or servers that are suspected of sending spam. Usually recipient email servers use blacklists to help decide whether they should accept or reject emails. In such cases, some emails you send from your IP address may never be delivered if your IP address has been blacklisted.
Your mail server IP will be blocked by the DNS blacklist monitor software if the RBL report states the IP is registered in the spam database. De-listing your IP may take days or even weeks. Anyone using software or firewalls will not receive your mail as your IP is considered blacklisted.
** Note that RBL (Realtime Blackhole List) is a website service that tracks the domain names or IP addresses where spam emails originate.
Why Domains are Blacklisted
1. Spam complaints from email recipients
Recipients can report emails as spam intentionally (they think the email is spam) or unintentionally (by clicking the "Spam" button instead of deleting the email). Some email recipients do not trust the unsubscribe option. They prefer to report the email as spam in order not to receive any more emails from this sender.
2. Kirim email ke alamat email trap spam
Beberapa ISP mengubah alamat email yang ditinggalkan menjadi kotak surat perangkap spam. Pesan apa pun yang dikirim ke alamat perangkap spam diperlakukan sebagai spam. Sebagian besar waktu alamat email perangkap spam dipenuhi dalam daftar email lama dan yang sudah dipanen. Jika Anda melihat daftar yang belum pernah Anda kirimi email selama satu atau dua tahun, kemungkinan berisi banyak email tidak valid dan perangkap spam seperti daftar yang Anda kumpulkan di Internet.
3. Bad server and IP reputation
If you don't have your own SMTP server and send emails from a shared mail server, your reputation depends on the reputation of that server. Sometimes ISPs blacklist entire IP ranges, if an IP address from your IP block is suspected in spam activity, your IP may be blacklisted as well. As you can see being blacklisted need not be the result of sending activity such as spam.
4. Site Application affected or Injected by Malware
Most viruses spread through email attachments, your IP may be affected once you click on a link or attachment. In the same way, the sites you visit may have malware hosted on their pages, it will send spam emails from your domain or IP to the recipient. Hence, you might blacklist the domain as the security trigger detects malicious activity.
How to Check Black List
Use a multi-blacklist search tool called MXToolbox or a free online blacklist check tool to check if your IP or domain is on the blacklist. If you find your domain listed, you can click on some suggestions or go to individual database services and find out their policies and procedures for removing your domain from the blacklist.
How to Prevent Black List
To keep your email out of the blacklist.
Use a static IP.
Prepare SPF or DKIM records.
Do not allow conveying.
Make sure you have a valid PTR record that matches your outgoing public IP to the mail server name and your hostname should resolve to the same IP address.
Make sure your server is not on the RBL list.
Enable SSL to encrypt the connection between the email client and the server.
Ask your subscribers to add your email address to their contact list.