AI email comparison
OpenAI (ChatGPT) vs DeepSeek for Email Drafting
DeepSeek is the cost play: OpenAI-compatible API, strong instruction-following, roughly an order of magnitude cheaper per token than GPT-4o. OpenAI is the safe default for idiomatic English and enterprise familiarity. DeepSeek's China-based inference is a hard stop for some regulated teams.
OpenAI (ChatGPT)
The most widely used AI assistant. Most ChatGPT-for-email power users start here, because it's the tool they're already tab-switching to.
OpenAI's consumer product is ChatGPT, but for email drafting the relevant distinction is between the free or Plus web app and the API. Plus subscribers get GPT-4o with custom instructions (a persistent system prompt you write once) and custom GPTs, which some professionals use as a rough style filter, though it requires re-pasting examples of your own writing and rarely holds up across a long thread. The API tier (GPT-4o, GPT-4o mini, and the o-series reasoning models) is what BYOK tools route through: pay per token, no chat history retained between calls unless the calling app manages it. ChatGPT Team and Enterprise add admin controls and a data-training opt-out, relevant for anyone drafting client-sensitive email. The practical gap for email specifically: ChatGPT has no concept of your Gmail or Outlook history, so every draft starts from whatever context you paste in, and default outputs lean toward a recognizable house style that recipients increasingly clock as AI-written.
Strengths for email
- Familiar interface; most users already have an account
- GPT-4o is strong at following complex style instructions
- Huge prompt-engineering community (r/ChatGPT, YouTube tutorials)
- Functions well as a catch-all AI for non-email tasks too
Weaknesses for email
- No persistent memory of your email style across sessions
- Requires manual copy-paste into Gmail or Outlook every time
- Generic outputs unless you write elaborate system prompts
- ChatGPT 'tells' (em-dashes, 'I hope this email finds you well') are widely detectable
Pricing: Free tier available; ChatGPT Plus ~$20/mo
Best for: General AI drafting when you want manual control over every word
DeepSeek
The Chinese open-source model that shocked the AI world with GPT-4 level performance at a fraction of the cost. Popular with BYOK users watching API pricing.
DeepSeek is an AI research lab that released a series of open-weight models, most notably DeepSeek-V3 (their flagship chat model), DeepSeek-R1 (a reasoning model competitive with o1), and DeepSeek-Coder-V2 (specialized for code generation tasks). The models use an OpenAI-compatible API format, which means any tool that accepts a custom endpoint and API key can route to DeepSeek with minimal configuration changes. For email drafting specifically, DeepSeek-V3 (accessed via the model name deepseek-chat) handles instruction-following and tone tasks well, though its training data skews toward Chinese-language text which can affect idiomatic English phrasing in subtle ways. The primary draw for BYOK users is cost: DeepSeek's API pricing is roughly 10-20x cheaper than GPT-4o at equivalent quality tiers, making it an attractive choice for high-volume drafting. The main concern for enterprise and regulated users is data residency: DeepSeek's inference servers are located in China, which creates compliance issues for organizations with strict data sovereignty requirements. Users who want DeepSeek's cost profile without the data residency risk typically run self-hosted versions via Ollama or a private cloud deployment.
Strengths for email
- Dramatically cheaper API pricing than OpenAI: roughly 10-20x less per token at comparable quality
- DeepSeek-V3 (deepseek-chat) is competitive with GPT-4o on instruction-following and email tasks
- DeepSeek-R1 (deepseek-reasoner) handles complex, multi-step reasoning comparable to OpenAI o1
- DeepSeek-Coder-V2 excels at code generation tasks
- OpenAI-compatible API format: works with any tool accepting a custom endpoint and one API key
- Open-source model weights available for self-hosting via Ollama or private deployment
- Excellent cost-performance ratio for BYOK users running high email volume
Weaknesses for email
- Data residency: inference servers are in China, a compliance risk for enterprise and regulated industries
- Training data skews toward Chinese-language text; subtle idiomatic gaps in English email prose
- Slow responses at peak load on the shared API; self-hosting resolves this but adds setup
- Less community support for email-specific prompting vs. the OpenAI ecosystem
- No native email client integration: requires copy-paste or a BYOK tool like ForthWrite
- Model weights are large; self-hosting requires significant hardware (GPU with 40GB+ VRAM for full precision)
Pricing: API: ~$0.14/M input tokens (DeepSeek-V3), ~10-20x cheaper than GPT-4o. Self-hosted: free, hardware costs only.
Best for: Cost-conscious BYOK users who want GPT-4 quality at a fraction of the API cost and can accept China-based data residency
Head-to-head for email
Verdict for email drafting
Choose DeepSeek when volume is high and data residency rules allow it. Choose OpenAI when compliance, English nuance, or existing vendor approval matter more than unit cost. Many BYOK users keep both keys and route by thread type.
Using OpenAI (ChatGPT) or DeepSeek inside your inbox
ForthWrite's BYOK path accepts DeepSeek and OpenAI side by side. High-volume acknowledgments can go to DeepSeek; sensitive client threads can stay on OpenAI, all from the same inbox widget and the same learned voice profile.
Both OpenAI (ChatGPT) and DeepSeek still start cold in a chat tab: no memory of your sentence length, openers, or sign-offs unless you re-paste a system prompt every session. ForthWrite learns from sent mail and drafts in Gmail or Outlook Web so the model choice is a setting, not a workflow.
Draft with the model you prefer, in your voice
Free plan includes voice matching and 10 drafts/week. Standard and Pro unlock BYOK across 9 providers, including the ones on this page.