How to Solve SMTP Error 421 4.4.5 – Server Congestion Issues
Email is key for both personal and professional lives. But when an email doesn’t make it to its recipient, it can cripple the business, lead to missed opportunities, and ultimately loss of revenue. Server congestion, or SMTP error 421 4.4.5, happens when an email server is overloaded with incoming or outgoing email requests. This might […]
SMTP Error 421 4.4.3 – Routing Server Failure Causes & Solutions
You may often see the error: SMTP transient error: 421 Service Not Available And think that you can just wait it out. This can be true for some of the SMTP email error 421, but its variants may have severe repercussions on your email deliverability. One of its variants that may require immediate attention is […]
SMTP Connection Encryption: The Key to Secure & Reliable Email Delivery
One of the top channels of communication for businesses is email, which unfortunately makes it one of the prime targets of cyberthreats like phishing, data interception, and spoofing. Encryption is the answer. Without it, emails are transmitted as plaintext over the Internet where people can steal sensitive information. SMTP (Simple Mail Transfer Protocol) is the […]
SMTP Error 421 4.3.2 – Service Shutting Down Causes & How to Fix It
There are tons of SMTP related errors that an average email user can encounter. Some of them can be due to IP reputation concerns, while others are rooted and are likely the result of a temporary errors failure — retryable errors. One of these temporary errors is the SMTP error 421 4.3.2 (Service Shutting Down), […]
How SMTP AUTH Mechanisms Affect Email Deliverability and Security
SMTP Authentication (SMTP AUTH) is not only a fundamental mechanism that protects your emails against spoofing and phishing attacks. It also has a direct contribution to your email deliverability and brand recognition. Depending on how well you set up your SMTP AUTH you are less likely to experience SMTP errors related to authentication failures —potentially […]
Reverse DNS Lookup Failures How They Impact Email Deliverability and Sender Trust
Email is a valuable communication channel, especially for many businesses and email marketers. It is known to develop the highest ROI, which should make inbox placement and email deliverability a priority.  The capability to ensure that your emails are delivered to the intended recipient is a simple idea, yet there are still some email users […]
SMTP Retries and Deferrals: Understanding Email Delays & How to Fix Them
The main protocol for sending email is the Simple Mail Transfer Protocol (SMTP), which manages both the sending and routing of messages between networked devices. But the journey from sender to recipient can sometimes be rocky. This may also result in SMTP retries/deferred by the senders. Though these mechanisms are supposed to be able to deal with […]
SMTP over IPv6: The Future of Email Servers and What It Means for Deliverability
The Simple Mail Transfer Protocol (SMTP)’s primary role is to make sure messages take the right path from senders to recipients. But with the world reeling with the internet boom, the traditional IPv4 system reached a point where it could no longer keep up. IPv4, the internet’s original addressing method, only has a limited number of […]
Maximizing Cold Email Impact: Social Proof and Email Deliverability
Can you remember the last thing you wanted to buy? Take a minute to think back to the moment leading up to the actual purchase. What did you do first? Chances are, you talked to people who made similar purchases. But knowing that someone bought the same thing (and is happy with their decision) is […]
What Is DNS Propagation and How to Minimize Its Impact on Email Deliverability
DNS records undergo modifications — such as SPF, DKIM, DMARC, MX, A records, or PTR records. These updates or modifications should propagate across global DNS servers, caching information a certain period before it refreshes. These modifications should not take longer than a few minutes to 48 hours. For rare and unusual circumstances these can take […]
