One of the most common questions among those who manage email campaigns is: "How can I be sure that everyone receives my emails?" The answer, unfortunately, is that there is no absolute guarantee. However, there are effective strategies to maximize deliverability — that is, the ability to get emails into the recipient’s inbox without being filtered as spam.
Successful delivery depends on technical factors, such as the configuration of authentication protocols, and the reputation of the sending IP address.
IP Reputation Monitoring and Blacklists
Maintaining a good IP reputation is essential. Blacklists are public tools that flag IP addresses suspected of sending spam. Being listed can seriously compromise deliverability. For this reason, it is advisable to regularly check whether your IP is listed in major blacklists.
Here is a list of the most authoritative blacklists you can check manually:
- Symantec (Broadcom): ipremoval.sms.symantec.com
- SenderScore: senderscore.org (registration required)
- Spamhaus: spamhaus.org
- Talos Reputation Center: talosintelligence.com
- Barracuda Central: barracudacentral.org
- Trendmicro: ers.trendmicro.com
- Reputation Authority: reputationauthority.org
- Cyren: cyren.com
- Abusix: abusix.ai
- MX Toolbox: mxtoolbox.com
- Proofpoint: ipcheck.proofpoint.com
- NiX DNSBL: dnsbl.manitu.net
Delisting: How to Get Off a Blacklist
If your IP address is found on a blacklist, you’ll need to initiate a delisting process. Each provider has its own procedure, but it usually involves submitting a form or opening a support request.
It’s crucial that any spam issues have been resolved before requesting delisting.
- Office 365: sender.office.com
- Microsoft (Outlook, Hotmail, Live, MSN): Support Form
- Microsoft SNDS: postmaster.live.com/snds
Email Authentication: SPF, DKIM and DMARC
SPF (Sender Policy Framework)
SPF specifies which servers are authorized to send email on behalf of the domain. It helps prevent spoofing and improves sender reputation.
SPF Check: dmarcanalyzer.com/spf/checker
DKIM (DomainKeys Identified Mail)
DKIM adds a digital signature to the email. The receiving server can verify that the message has not been altered and that it really originates from the stated domain.
DMARC (Domain-based Message Authentication, Reporting and Conformance)
DMARC combines SPF and DKIM, and tells receiving servers how to handle emails that fail authentication checks.
- Confirms the sender’s identity
- Defines policies for failed authentication
- Requests reports on suspicious emails
Sample DMARC DNS record:
_dmarc.yourdomain.it TXT "v=DMARC1; p=none; rua=mailto:webmaster@yourdomain.it; ruf=mailto:webmaster@yourdomain.it"
IP Warm-Up: Building a Positive IP Reputation
When using a new sending IP address, it is essential to follow a gradual warm-up process. This process, known as IP warm-up, involves progressively increasing the volume of emails sent, starting with small batches.
ISPs evaluate IP behavior. A sudden spike in volume from a new IP is often flagged as suspicious. Warming up gradually helps build trust and improve delivery rates.
Note: It’s much easier to build a good reputation than to recover a damaged one.
Other Essential Rules
- Avoid hard bounces: remove invalid email addresses to prevent penalties. Repeatedly sending to non-existent recipients lowers sender reputation.
