How to clean and import your B2B contact lists into Mailforge for maximum deliverability

If you’ve ever tried to send a B2B campaign and ended up in spam, you know the pain. Bounced emails, angry replies, or worse—getting your sender reputation trashed. Whether you’re a marketer, SDR, or just someone who inherited a sketchy old CSV, this guide’s for you. We’ll walk through how to clean up your contact list, prep it properly, and import it into Mailforge so you actually reach inboxes—not junk folders.

1. Why List Hygiene Actually Matters (And What to Ignore)

Let’s get this out of the way: dumping a giant, stale spreadsheet into an email platform is a recipe for disaster.

Here’s what happens if you skip the cleanup: - You hit spam traps and dead addresses, tanking your sender score. - Campaigns get throttled, delayed, or blocked entirely. - You annoy real prospects with bad info or duplicate emails. - Your “open rates” become meaningless.

What doesn’t matter as much as people say? - Fancy segmentation and tagging—if the base list is dirty, no amount of slicing will save it. - Chasing “AI-powered” cleanup tools—most use the same basic validation APIs.

Bottom line: good hygiene beats fancy features every time.

2. Step 1: Get Your List in Order

Before you even touch Mailforge, you need to know what’s in that file. If you’re working with a list from sales, marketing, or some “downloaded from LinkedIn” source, assume there’s junk.

What to look for: - Obvious duplicates (same email, same domain) - Personal email addresses (gmail, yahoo, etc.—these are rarely useful in B2B) - Missing names (first name, last name, or company—blank fields are a red flag) - Weird formatting (multiple emails in one cell, odd characters)

Pro tip: Open the file in Excel or Google Sheets, not just Notepad. It's much easier to spot weirdness in a table.

3. Step 2: Remove the Junk

Now, actually clean up the data. Don’t overthink it—just focus on what matters for deliverability.

a) Dedupe ruthlessly

  • Use the “Remove Duplicates” tool in your spreadsheet software.
  • For B2B, de-dupe by email address at a minimum.
  • If you have multiple contacts at the same company, make sure you’re not emailing the same person twice.

b) Delete obvious bad actors

  • Any row with a blank or malformed email address? Gone.
  • Emails that are clearly typos (e.g., “@gmaill.com”)? Delete or fix.
  • Rows with “info@”, “sales@”, or “admin@” are risky—they’re often ignored, or worse, spam traps.

c) Filter out role-based or catch-all addresses

  • “support@”, “contact@”, “webmaster@”—these are rarely tied to a real person.
  • If you must keep them, tag them separately so you can exclude from key sends.

4. Step 3: Run a Deliverability Check

No matter how good your spreadsheet skills are, you can’t eyeball a spam trap. This is where validation tools come in.

Recommended tools (they’re all similar, don’t get distracted by hype): - NeverBounce - ZeroBounce - BriteVerify - Clean Email List (for smaller budgets)

What to look for in a validator: - “Invalid” or “do not send” results—remove these entirely. - “Catch-all” or “unknown” results—these are a gamble. If you’re risk-averse, exclude them; if you’re desperate for volume, keep them but monitor your bounce rate closely. - “Disposable” or “temporary” emails—delete.

Honest tip: Don’t bother paying extra for “enrichment” or “AI scoring.” Focus on list hygiene, not wishful thinking.

5. Step 4: Format for Mailforge Import

Mailforge isn’t magic—it expects a clean, simple CSV file. Here’s how to prep it:

Basic checklist: - Save as CSV (comma-separated values). Not XLSX, not Google Sheets, not “Tab-delimited.” - Column headers should be simple: email, first_name, last_name, company (all lowercase, no spaces or weird punctuation). - Remove extra columns you don’t need. If you’re not going to use “Twitter handle” or “Notes”, delete the columns. - Make sure there are no blank rows at the end of your file.

Quick sanity check: - Open the CSV in Notepad or TextEdit. You should see clean, comma-separated values, no stray quote marks or weird symbols.

6. Step 5: Import Into Mailforge

Now you’re ready to bring your list into Mailforge:

a) Log in and go to the Contacts section

  • Click “Import Contacts” or similar (they move buttons sometimes, but it’s usually obvious).
  • Choose “Upload CSV” and select your cleaned file.

b) Map your fields

  • Mailforge will ask you to match columns in your CSV to fields in their database.
  • Make sure email is mapped to “Email”, first_name to “First Name”, etc.
  • If you see any “unmatched” fields, ignore them or map as needed.

c) Set your opt-in status

  • Only import contacts you have permission to email.
  • If you’re not sure, err on the side of caution. Import as “Unsubscribed” and reconfirm later if needed.

d) Let the import finish

  • Mailforge will show you errors or rejected rows. Download these and review—don’t just ignore them.
  • If you see a high error count, your CSV probably still has formatting issues. Go back, fix, and re-upload.

Don’t: - Try to sneak in a 100k list all at once if you’re new to Mailforge. They’ll notice, and your account could get flagged. - Import cold contacts and blast them right away. Warm up your list with smaller batches first.

7. Step 6: Warm Up and Monitor (Don’t Skip This!)

You’re not done just because the contacts are in Mailforge. The first few sends are critical.

Best practices: - Start with a small, high-quality segment. People you know, or those who’ve engaged with you before. - Watch your bounce and spam complaint rates. If you see >2% bounces, pause and review your list again. - Gradually increase your send volume over a week or two. This helps you avoid spam filters and keeps your domain healthy.

If things go wrong: - High bounces? Go back to your validator—your list wasn’t as clean as you thought. - Lots of unsubscribes or spam complaints? Your messaging or targeting might be off. Don’t just blame the list.

8. Common Pitfalls (And What to Ignore)

Let’s be real—most B2B lists are messy. You can’t fix everything, but you can avoid the big mistakes:

Don’t waste time on: - Fancy enrichment tools that promise “fresh leads”—most just resell stale data. - Segmenting a dirty list into a dozen micro-niches. Clean first, segment later. - Chasing zero bounces. Some will always slip through—just keep it under 2%.

Do focus on: - Permission and relevance. Don’t cold-email randoms who never asked for it. - Ongoing hygiene. Clean your list quarterly, not just once. - Keeping your CSVs simple and well-formatted.

Keep It Simple and Iterate

Cleaning and importing your B2B list into Mailforge isn’t rocket science, but it does take a little discipline. Resist the urge to get fancy until you’ve nailed the basics: accurate data, proper validation, and slow, steady sending. If you get stuck, back up and simplify. The best senders aren’t the ones with the most expensive tools—they’re the ones who keep their lists clean and their processes boring.

Good luck, and remember: clean data beats clever tricks, every time.