To optimize email deliverability and engagement, avoid spam trigger words ('free,' 'urgent'), misleading subject lines, lack of personalization, excessive capitalization/punctuation, false promises, clickbait tactics, and URL shorteners. Adhere to email standards, avoiding specific characters that cause parsing issues. Use concise subject lines (around 50 characters), A/B test, use supported characters and preheader text. Proper authentication is key. Be wary of outdated advice like the pink background/AOL myth.
10 marketer opinions
Email subject lines should avoid spam trigger words, misleading content, lack of personalization, excessive capitalization/punctuation, false promises, and clickbait tactics. Concise subject lines (around 50 characters) are best for mobile readability. A/B testing, proper character usage, and utilizing preheader text are recommended for optimization.
Marketer view
Email marketer from Email on Acid explains that neglecting preheader text is a missed opportunity; use it to supplement the subject line.
21 Oct 2024 - Email on Acid
Marketer view
Email marketer from Email Marketing Forum explains that making false promises or exaggerating claims in subject lines can lead to distrust and unsubscribes.
14 Aug 2023 - Email Marketing Forum
6 expert opinions
Email subject lines should avoid spammy words like 'FREE' and excessive punctuation (!!!). Misleading subject lines are harmful. Using all caps can trigger spam filters. URL shorteners are suspicious. A/B testing is useful. Old advice about pink backgrounds and AOL blocking is no longer valid.
Expert view
Expert from Email Geeks shares that you shouldn’t use FREE or !!! in the subject line, based on something read on the internet.
25 Feb 2024 - Email Geeks
Expert view
Expert from Spam Resource shares that using all caps in subject lines is generally seen as shouting and can trigger spam filters.
30 Dec 2021 - Spam Resource
3 technical articles
Email subject lines should adhere to email standards and avoid certain characters and formatting practices that could cause parsing or display issues. Avoiding spam triggers and ensuring proper authentication also helps improve deliverability.
Technical article
Documentation from Microsoft Documentation explains that adhering to email standards (like avoiding certain characters and encoding issues) is important for deliverability.
26 May 2022 - Microsoft Documentation
Technical article
Documentation from RFC Editor explains that certain characters and formatting practices should be avoided as they could cause issues with email parsing and display in some systems.
27 Feb 2023 - RFC Editor
Are spam trigger word lists accurate and should I be concerned about them?
Are spam trigger word lists still relevant for email deliverability?
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How does subject line length affect email deliverability and click-to-open rates on Yahoo and AOL?
Is it a good idea to put an email address in the subject line?
What words and phrases are considered spammy and trigger spam filters?