Why Connect Your Own SMTP Accounts

The main reason Bulko requires you to connect your own SMTPs, rather than sending from a shared IP, is reputation. When multiple clients send through one shared IP, the actions of one careless user ruin deliverability for everyone else.

How SMTP Reputation Works

Email providers (Gmail, Outlook, Yahoo, Mail.ru) track every sender's IP address. They look at:

• Sending volumes (a sudden spike is suspicious)
• Bounce rate (% of emails to non-existent addresses)
• Spam complaints (% of recipients who marked as spam)
• Engagement (opens, clicks, replies)

Based on this data, the IP receives a score from 0 to 100. If the score falls below a certain threshold, the provider starts putting emails in spam or even discarding them without delivery.

The Problem with Shared IPs

In classic ESPs (Mailchimp, SendGrid), hundreds of clients send through one shared pool. One client sent 10K emails to a purchased list with a 30% bounce rate — the IP reputation drops, and all other clients in this pool receive a higher-than-normal bounce rate.

The constant struggle of ESPs is to balance pools and block malicious clients before they ruin the reputation. It doesn't always work out.

The Advantage of Your Own SMTPs

When you connect your own Gmail account or Amazon SES, the reputation is entirely yours. No one else can spoil it. If you follow the rules (warm-up, reasonable volumes, clean list) — deliverability is consistently high.

Which SMTP to Choose

• Gmail Workspace — excellent reputation, limit of 2000 emails/day, requires App Password. Suitable for small volumes and starting out
• Microsoft 365 (Outlook) — good reputation in B2B, limit of 10000 emails/day, has authentication nuances
• Amazon SES — very cheap ($0.10/1000), requires exiting sandbox mode, you need to build reputation from scratch. Ideal for large volumes
• SendGrid / Mailgun — easier to set up than SES, but more expensive. Good default limits
• Warmed-up dedicated accounts — you buy a ready-made SMTP with a high reputation from resellers. The fastest way to large volumes, but you need to know the supplier

Multiple SMTPs Are Better

Bulko automatically distributes the load between all your SMTPs. If you have 5 Gmail accounts with a limit of 200/day, you can send 1000 emails a day without any risk to your reputation. If you have one Amazon SES with a limit of 50K/day — 50K emails in one day.

Next: warming up new SMTPs, or directly guides on setting up popular providers.