What are the essential parts of an email address?
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An email address has two halves split by an @ symbol. The part before the @ is the local part (also called the username or mailbox name). The part after is the domain. Example: kraken@deepseamail.com means kraken is the local part and deepseamail.com is the domain.
The @ symbol is just the separator. Ray Tomlinson picked it in 1971 because it meant "at" and nobody was using it in names. Now it's everywhere (there's one in the Museum of Modern Art's permanent collection).
The domain is where things get interesting for deliverability. When you send email from captain@harborpost.net, receiving mail servers look up harborpost.net to find where the mail should come from. That lookup happens through DNS records like SPF and DKIM. If your domain doesn't have those records set up correctly, your emails fail authentication checks and land in spam (or bounce entirely).
The local part matters less for authentication but more for reputation. Mailbox providers like Gmail and Outlook track engagement per sender address. If noreply@yourdomain.com sends all your marketing email and gets ignored or marked as spam, that address builds a bad reputation. Using a real person's name (like support@ or hello@) often gets better engagement because it feels human.
One practical mistake: using different domains for different types of email without thinking through authentication. If your marketing campaigns come from @marketing.yourbrand.com but your transactional emails come from @yourbrand.com, you need separate SPF and DKIM records for both. Miss one and half your email breaks.
But the TLD (the .com or .org or .io part) used to matter a lot for trust. These days, as long as it's a real TLD and not something sketchy like .top or .xyz (common in spam), you're fine. Country-code TLDs like .uk or .de are perfectly fine if that's where your business actually operates.
Want to check if your domain is set up correctly? Run it through our free SPF checker and DKIM lookup tool. Takes 30 seconds and catches most authentication mistakes before they cause delivery problems.
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