Even with a perfect technical setup, a single “spammy” phrase or a broken link can ruin your deliverability. Before you send your campaign to thousands of people, you should always run it through a spam checker to see exactly how email filters will grade your content.
1. Why Use a Spam Checker?
Spam filters like SpamAssassin or Gmail’s internal AI look at dozens of factors simultaneously. A spam checker simulates these filters and gives you a score.
- Detect Hidden Issues: It finds broken links, missing Alt-text on images, or blacklisted URLs.
- Authentication Check: It double-checks if your SPF, DKIM, and DMARC are actually working on that specific email.
- Content Analysis: It flags words that are statistically likely to trigger filters (e.g., “Weight loss,” “Make money fast,” “Act now”).
2. Recommended Tools
While Sendonyx provides internal previews, we recommend using these third-party industry standards for a deep dive:
- Mail-Tester.com: The gold standard. You send your email to a unique address, and it gives you a score out of 10.
- Litmus / Email on Acid: Best for checking how your email looks on different devices (iPhone, Outlook, Gmail Desktop).
- GlockApps: Excellent for checking which specific tab (Primary, Promotions, or Spam) your email lands in.
The 9/10 Rule: When using Mail-Tester, never send a campaign if your score is below 9. If you get a 7 or an 8, read the breakdown and fix the specific issues mentioned—usually, it’s a simple fix like an unoptimized image or a suspicious link.
3. Common “Red Flags” Found by Checkers
When you run a check, keep an eye out for these frequent mistakes:
- Shortened URLs: Avoid using Bitly or TinyURL. Spammers abuse these, so filters often block any email containing them. Use full URLs or your own branded tracking links.
- Subject Line All Caps: Writing “OPEN NOW” is an instant penalty.
- HTML Errors: Unclosed tags or “messy” code from Word/Google Docs can confuse filters.
Don’t Forget the Text Version: Every HTML email should have a plain-text alternative. Sendonyx creates this for you, but make sure it’s not empty. Emails without a plain-text version are a major spam signal.