This page lists and tries to explain errors you may have received while attempting to
deliver messages to our servers. Some errors also provide tips for you to remediate the block.
The SMTP response you received contains a unique code starting with
OXSUS_; Find the code below to spot the block reason you are
experiencing.
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OXSUS00X_101
-
550 5.7.1 Connection refused
- We could not accept your email because your email provider is listed on the Vade
Secure Threat Network list.
-
This list contains IP addresses which have been identified as sending spam. We use this
list to protect our subscribers from receiving spam.
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OXSUS00X_102
-
550 5.7.1 Connection refused
- We could not accept your email because your email provider is listed on the Validity Blocklist.
Please go to https://senderscore.org/blocklist-lookup/ to get unlisted
-
This list contains IP addresses which have been identified as sending spam. We use this
list to protect our subscribers from receiving spam.
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OXSUS00X_103
-
421 4.2.1 Connection deferred
- We could not accept your email at that moment because the server is experiencing
issues
delivering to backend servers. There are too many messages in queue at the moment. You may
retry delivering the message at a later time.
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OXSUS00X_105
-
550 5.7.1 Connection refused
- Reject if reverse dns is not present
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OXSUS00X_110
-
421 4.2.1 Connection refused
- We could not accept your email because the email provider has opened too many
connections from a single IP address. The message may be retried using a different SMTP
session.
-
OXSUS00X_130
-
421 4.2.1 Connection refused
- Our servers protect our users by checking the spam ratio that was received from
your
mail delivery system over a given time period. This message informs you that your mail
delivery system has exceeded the spam ratio over a given period of time, and that the
message may be retried at a later time.
-
OXSUS00X_133
-
421 4.2.1 Connection refused
- Our servers protect our users by checking the number of invalid recipients over a
given
time period. This message informs you that your mail delivery system has reached the
maximum number of bad recipients over a given period of time, and that the message may be
retried at a later time.
-
OXSUS00X_136
-
421 4.2.1 Connection refused
- Our servers rate limit all inbound email traffic, in order to protect our customers
and
our email infrastructure from attacks. This message informs you that the IP address of the
mail delivery system has reached its limit by sending too many messages, and that the
message may be retried at a later time.
-
OXSUS00X_139
-
421 4.2.1 Connection refused
- Our servers rate limit all inbound email traffic, in order to protect our customers
and
our email infrastructure from attacks. This message informs you that the IP address of the
mail delivery system has reached its limit by opening too many connections, and that the
message may be retried at a later time.
-
OXSUS00X_140
-
421 4.2.1 Connection refused
- Our servers rate limit all inbound email traffic, in order to protect our customers
and
our email infrastructure from attacks. This message informs you that the IP address of the
mail delivery system has reached its limit by sending too many messages, and that the
message may be retried at a later time.
-
OXSUS00X_142
-
421 4.2.1 Connection refused
- Our servers protect our users by checking the number of recipients your mail
delivery
system sent messages to over a given time period. This message informs you that your mail
delivery system has reached the maximum number of recipients over a given period of time,
and that the message may be retried at a later time.
-
OXSUS00X_201
-
550 5.7.1 Connection refused
- We could not accept your email because your email provider is listed on the Vade
Secure
Threat Network list.
-
This list contains IP addresses and FQDNs which have been identified as sending spam.
We use this list to protect our subscribers from receiving spam.
-
OXSUS00X_203
-
550 5.7.1 Connection refused
- We could not accept your email because it failed to pass SPF verification for the
sending domain. For more information on troubleshooting this, please refer to https://tools.ietf.org/html/rfc7208.
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OXSUS00X_301
-
550 5.7.1 Connection refused
- We could not accept your email because the format of the sender address provided as
part
of the MAIL FROM command is invalid.
-
OXSUS00X_303
-
421 4.2.1 Connection refused
- We could not accept your email because the sender domain is invalid or could not be
verified: i.e. we were not able to resolve that domain to an A or MX DNS record.
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OXSUS00X_304
-
550 5.7.1 Connection refused
- We could not accept your email because the domain used in the From:
header either does not match the MAIL FROM address or the
SPF record.
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OXSUS00X_305
-
421 4.2.1 Connection deferred
- Our servers protect rate limit the number of transactions allowed in a single SMTP
session in order to protect our users and infrastructure. The current limit is set to 50
transactions per session. You may retry to deliver the message using a new session.
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OXSUS00X_403
-
550 5.7.1 Connection refused
- We could not accept your email because the message was sent to a non-existent
customer/user. These errors should be treated as an "unsubscribe" by the sender, if a bulk
mailer.
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OXSUS00X_404
-
421 4.2.1 Connection refused
- Our servers protect rate limit the number of recipients per message allowed in a
single
SMTP session over a given period of time in order to protect our users and infrastructure.
You may retry to deliver the message at a later time.
-
OXSUS00X_405
-
421 4.2.1 Connection refused
- We could not accept your email because it exceeds the number of recipients allowed
for a
single message. The current limit is set to 150 recipients.
-
OXSUS00X_406
-
550 5.7.1 Connection refused
- We could not accept your email because the format of the recipient's address
provided as
part of an RCPT TO command is invalid.
-
OXSUS00X_503
-
550 5.7.1 Connection refused
- We could not accept your email because it does not contain the mandatory
From:
header, or it was empty.
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OXSUS00X_507
-
550 5.7.1 Message rejected
- We could not accept your email because it failed to pass DKIM authentication for
the
sending domain. For more information on troubleshooting this, please refer to https://tools.ietf.org/html/rfc5585.
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OXSUS00X_510
-
552 5.3.4 Message size limit exceeded
- We could not deliver your email because it exceeds the maximum size allowed on our
servers, which is currently set to 28MB (
29360128 bytes).