Reading time: 4 minutes
Blocking or blacklisting entire Top Level Domains (TLDs) used for hostname in email server setup can be a very effective solution to stop low reputation mail servers delivering mails to your email system(s).
As most email providers use common TLDs like .net, .com
or .de in their email setup, you can selectively block new or low reputation
TLDs and this way reducing a lot of unwanted emails.
Reading time: 4 minutes
Blocking or blacklisting entire Top Level Domains (TLDs) in Postfix mail server may have a big impact to reduce spam, phishing, and other unwanted emails. Dependent on the use case of your systems it is a valid and effective solution. The only drawback is, to monitor your email traffic and check, whether valid emails from blocked TLDs are sent to your systems. Blocking a whole TLD is mostly a temporary thing, as the bad guys move on if the domains on a specific TLD are not usable for their cases.
Reading time: 3 minutes
Sending a test email from shell using command line, send mails in shell script is a common task for an email admin. Mails were and still are used to inform admins regarding changes, warnings and problems.
Dependent on the task you want to achieve, some content should be in the body of an email or attached as file. Let’s figure out, how to do it using Linux or Unix command line like bash or zsh.
Reading time: 7 minutes
You have built your local IP blacklist for Postfix. Invested time to analyze server logs or Rspamd history to blacklist single hosts, IP addresses, or even whole networks. But how well is it working compared to public blacklists you are using? Time to see the results and get some visual insights through Munin Monitoring System.
First of all, you have to decide how to visualize the data in your graph. There are different solutions you can approach. You may want so kind of overview, to see how many hits your blacklist has. Maybe you want to monitor or compare the results to public or payed blacklists you are using.
Reading time: 7 minutes
By running a Postfix mail server, you need to know some commands to manage Postfix mail queues. With this knowledge, you can manage queues and write simple scripts to accomplish larger tasks.
First, I will list the most relevant commands you need for your daily business. Then we will build up real-life examples to understand how these commands work, how to use them, and when they can harm.
Reading time: 4 minutes
You know those same hosts, providers, or whole networks, who get through your spam filter and spam your users with the same content over and over again. By building up your blacklist in Postfix, you can stop them from bothering you and your users. We will explain how local blacklists work in Postfix and how to use them with whitelists to have better control and reduce errors.
Blocking other hosts must be a well-thought decision because blocking single hosts, IP addresses, or even whole networks will stop all delivery attempts to your mail servers.
Reading time: 3 minutes
If you use any blacklists for email services, whitelisting important Hosts, single IP Addresses, and even whole networks is an essential task. By whitelisting valuables email services to your users or even customers, you as admin won’t reject important email communication.
If you use any blacklist service or has your blacklist in your Postfix setup, you will probably find similar logs:
root@server $ grep "blocked using" /var/log/mail.log
Dec 17 4:07:18 server postfix/smtpd[21213]: NOQUEUE: reject: RCPT from
unknown[1.2.3.4]: 554 5.7.1 Service unavailable; Client host [1.2.3.4]
blocked using ix.dnsbl.manitu.net; Blocked - see http://www.dnsbl.manitu.net/lookup.php?value=1.2.3.4;
from=<x0h0ihbxazf@somedomain.example> to=<cp57ouwn7zm9@mydomain.example> proto=ESMTP helo=<[1.2.3.4]>
As you can see in this example, IP Address 1.2.3.4 was blacklisted by a third-party service.
Reading time: 6 minutes
Monitoring email queues on your favorite email server is an essential task of an email admin, as rising queues are often an indication of problems. First, you need to understand how queues work, manage them, and get emails enqueued. Then build a shell script to monitor them. In the last step, you will learn how to get smartphone push notifications by sending emails to a third-party push service.
Reading time: 3 minutes
One of the most critical parts of MailMum is to provide DNS service, which handles IP blacklisting for our customers. They are the primary service our customer’s mail servers are using.
As the DNS flag day 2020 directed to operational and security problems in DNS caused by Internet Protocol packet fragmentation, we’ve tested all our DNS services to align these rules.
DNS is a distributed system and one of the most critical parts of networks. If DNS fails; most services stop working as they rely on DNS resolution. Most companies run at least one DNS server our use a provided DNS server for their company. Some run thousands to offer their employee and their customers DNS services.
Reading time: 5 minutes
Providing email services to your customers or even your own company is an import part of communication. Also, it is important to brand your service and this way also adds some additional trust for your users. Roundcube Support pleases admins to customize their installation, so the people don’t contact Roundcube project for support.
Selecting the right skin for your users is a hard task. Even if the webmail services you provide, are only for one company. Dependent on your users you have to decide, how the webmail should look like.
Reading time: 2 minutes
Certificates today are like DNS - they must work, because most of the systems expect them to be there and they must be valid. Especially Google changed for many services to contact with SSL/TLS enabled by default.
Sometimes problems arise and you need to check whether certbot (of Let’s Encrypt) or cron is still working. Maybe you simply want to check, whether your certificates are all renewed, you can simply run:
Reading time: 3 minutes
A name, domain, logo, and a draft website - this is the way MailMum was born out of an internal project.
MailMum was born out of a need to face problems with unwanted emails called spam or junk. As filters like Spamassassin were good, but spammers are human, their job is to figure out how to bypass them. They will try and will find ways to reach your inbox.