Format and Syntax Issues

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These can often be identified through basic spreadsheet functions or email validation tools:
consecutive periods ("john..doe@example.com").
Typos in Common Domains: Look for common sweden email list These are often "typo traps" used by ISPs.
B. Behavioral and Performance Indicators (Post-Send):
These metrics, visible in your Email Service Provider (ESP) reports, are crucial for identifying list quality issues:

High Bounce Rates:
Hard Bounces: These are permanent delivery failures (e.g., "address doesn't exist," "domain not found"). A high hard bounce rate (consistently over 2%) is a strong indicator of a poor-quality list or a list containing many old, defunct addresses or spam traps.

Soft Bounces: Temporary failures (e.g., "mailbox full," "server temporarily unavailable"). While less critical, a consistently high soft bounce rate for particular addresses can also indicate issues.
High Spam Complaint Rates: If a significant number of recipients mark your emails as spam (generally above 0.1%), it's a huge red flag. This tells ISPs that your messages are unwanted, severely damaging your sender reputation. Purchased lists are notorious for this.
Low Open Rates: If your open rates are significantly below industry averages (which vary by industry, but often hover around 15-25%), it suggests that your emails aren't reaching inboxes (deliverability issues) or that the recipients aren't interested.
Low Click-Through Rates (CTR) & Conversion Rates: Even if emails are opened, if very few people click on links or convert, it indicates a lack of interest or relevance among your subscribers, common with untargeted, fake lists.