334
SMTP
334 Server Challenge
The server is issuing an authentication challenge as part of the SASL authentication exchange. The response contains a Base64-encoded challenge that the client must decode and respond to.
このコードが表示される場合
During the AUTH command handshake. The server is prompting you for your username or password (Base64-encoded) as part of the multi-step authentication process.
解決方法
Respond with the appropriate Base64-encoded credentials. If authentication keeps failing after responding, verify your credentials and ensure you are using the correct SASL mechanism.
比較対象
ガイド
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Diagnosing Email Bounces: Soft (4xx) vs Hard (5xx)
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DNS Record Types Explained: A, AAAA, CNAME, MX, TXT, and Beyond
DNS & Networking
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DNS & Networking
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用語集
Status Code
Media Type (MIME Type)
TLS Handshake
TLS Certificate (SSL Certificate)
Cipher Suite
Authentication
TCP/IP
Three-Way Handshake
Port Number
Firewall
IPv6
Exponential Backoff
Error Code Mapping
Poison Message
Request-Response Model
RFC (Request for Comments)
IANA (Internet Assigned Numbers Authority)
Message Framing
Connection-Oriented
Text vs Binary Protocol
MX Record
PTR Record
SMTP Relay
SPF, DKIM, and DMARC
Bounce Rate (Email)
Email Deliverability
MTA (Mail Transfer Agent)
SMTP Pipelining
Greylisting
Backscatter
Envelope vs Header
STARTTLS
SMTP Authentication (SMTP AUTH)
Open Relay
Email Queue
MIME Multipart
ARC (Authenticated Received Chain)
BIMI (Brand Indicators for Message Identification)
DSN (Delivery Status Notification)
Email Header Injection
SMTP Enhanced Status Codes
MDN (Message Disposition Notification)
MIME Type
TLS Versions
TLS 1.3
Certificate Authority (CA)
Forward Secrecy (PFS)
SNI (Server Name Indication)
TLS Session Resumption
Key Exchange
PKI (Public Key Infrastructure)