8 Communication APIs with verified auth, pricing and rate limits. 8 offer a free tier; 1 document an MCP server. Every field carries the source URL that states it.
| API | Category | Auth | Pricing | MCP | Free | Confidence |
|---|---|---|---|---|---|---|
| PostStack poststack.dev | Communication | bearer_token | freemium | ● | ● | high |
| Kiprio Email Validate kiprio.com | Communication | api_key | freemium | — | ● | high |
| UserCheck (formerly MailCheck.ai) mailcheck.ai | Communication | bearer_token | freemium | — | ● | high |
| Mail.tm mail.tm | Communication | bearer_token | free | — | ● | medium |
| mailboxlayer mailboxlayer.com | Communication | api_key | freemium | — | ● | medium |
| Mailchimp mailchimp.com | Communication | api_key | freemium | — | ● | medium |
| Postmark Account-level API postmarkapp.com | Communication | api_key | freemium | — | ● | medium |
| BulkSMS JSON REST API bulksms.com | Communication | — | usage_based | — | ● | medium |