The problem with post-generation regex filters
Traditional keyword blocklists are too brittle to catch nuanced AI hallucinations or policy violations. An agent offering an unauthorized 80% discount might not use the word "discount", phrasing it as "we have updated your annual invoice to $20".
Semantic routing evaluates the vector embedding of the drafted message against predefined semantic clusters (e.g. Financial Promises, Legal Claims, Standard Support, Password Reset) with sub-10ms latency.
Building a Semantic Email Router in Python
Using the open-source semantic-router library with local embeddings (such as HuggingFace MiniLM or Cohere), we classify outbound messages before hitting the send API.
from semantic_router import Route
from semantic_router.encoders import HuggingFaceEncoder
from semantic_router.layer import RouteLayer
import requests
# 1. Define high-risk semantic clusters
financial_route = Route(
name="financial_risk",
utterances=[
"We are refunding your full subscription cost.",
"Your new discounted rate is $5 per month.",
"I have credited $500 back to your account.",
"You do not need to pay the remaining invoice balance."
]
)
standard_support = Route(
name="standard_support",
utterances=[
"Here are the instructions to reset your password.",
"Your support ticket #4102 has been received.",
"Please find the user manual attached.",
"Our office hours are 9 AM to 5 PM EST."
]
)
encoder = HuggingFaceEncoder(name="sentence-transformers/all-MiniLM-L6-v2")
router = RouteLayer(encoder=encoder, routes=[financial_route, standard_support])
def dispatch_safely(recipient: str, subject: str, draft_text: str):
decision = router(draft_text)
if decision.name == "financial_risk":
print(f"[ESCALATION] Message flagged for human financial approval: '{draft_text}'")
# Enqueue for manual supervisor sign-off
return {"status": "queued_for_approval"}
# Safe to dispatch autonomously
res = requests.post(
"https://api.sadasend.com/v1/emails",
headers={"Authorization": "Bearer sada_live_sk_..."},
json={"to": recipient, "subject": subject, "text": draft_text}
)
return res.json()Key architectural advantages
- Sub-15ms local inference latency: Zero external API round-trips for classification.
- Zero false positives on common synonyms: Embeddings understand context rather than exact words.
- Auditable policy enforcement: Every routing decision can be logged and tuned over time.
Building AI agents that send email?
Join the SadaSend early access waitlist to get scoped API keys, recipient allowlists, and Model Context Protocol (MCP) servers upon launch.