- A
Port 80
Why wrong: Port 80 is used for HTTP web traffic, not email submission.
- B
Port 443
Why wrong: Port 443 is used for HTTPS secure web traffic.
- C
Port 587
Port 587 is the standard SMTP submission port for outgoing email.
- D
Port 110
Why wrong: Port 110 is used for POP3 to receive email, not send.
Question 908 of 1,020
SMTP Port: 587 for Email Submission
This 220-1201 practice question tests your understanding of tcp & udp ports. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A customer reports that they can browse the internet but cannot send or receive emails using their desktop email client. The email server is known to be working. Which port is most likely being blocked by a firewall?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"most likely"Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Quick Answer
The answer is port 587, the standard port for SMTP email submission with STARTTLS encryption. When a customer can browse the internet but cannot send or receive emails, it typically indicates a firewall is blocking the specific port used for outgoing mail, while leaving web ports like 80 and 443 open. Port 587 is the modern, recommended port for email clients to submit outgoing messages securely, whereas port 25 is often blocked by ISPs to prevent spam. On the CompTIA A+ Core 1 220-1201 exam, this scenario tests your understanding of common port numbers and their associated services—a frequent trap is confusing SMTP ports with receiving ports like 110 (POP3) or 143 (IMAP). Remember, web browsing works on ports 80 and 443, but email submission requires its own dedicated port. A simple memory tip: think of “587” as “5-8-7, I send to heaven”—the secure way to send your email out.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Port 587
Port 587 is the standard SMTP submission port (RFC 6409) used by email clients to send outgoing mail. Since the user can browse the internet (ports 80/443 are open) but cannot send or receive emails, a firewall blocking port 587 would prevent the email client from submitting outgoing messages to the server, while leaving web traffic unaffected. The email server is confirmed working, so the issue is likely a blocked outbound port on the client's firewall.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Port 80
Why it's wrong here
Port 80 is used for HTTP web traffic, not email submission.
- ✗
Port 443
Why it's wrong here
Port 443 is used for HTTPS secure web traffic.
- ✓
Port 587
Why this is correct
Port 587 is the standard SMTP submission port for outgoing email.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Port 110
Why it's wrong here
Port 110 is used for POP3 to receive email, not send.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Candidates often mistakenly think that SMTP uses only port 25, but many ISPs and firewalls block port 25 to prevent spam. Port 587 is the standard submission port for email clients. Additionally, port 110 (POP3) is for receiving email, not sending.
Detailed technical explanation
How to think about this question
SMTP submission on port 587 requires STARTTLS for encryption, as defined in RFC 3207, and is distinct from the traditional SMTP port 25 which is often blocked by ISPs to prevent spam relaying. In real-world scenarios, corporate firewalls may block outbound port 587 while allowing web ports, causing email clients to fail silently unless configured to use port 465 (SMTPS) or an alternative submission method. The email client's SMTP server settings must explicitly specify port 587 for submission to work through a restrictive firewall.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A practitioner preparing for the 220-1201 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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FAQ
Questions learners often ask
What does this 220-1201 question test?
TCP & UDP Ports — This question tests TCP & UDP Ports — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Port 587 — Port 587 is the standard SMTP submission port (RFC 6409) used by email clients to send outgoing mail. Since the user can browse the internet (ports 80/443 are open) but cannot send or receive emails, a firewall blocking port 587 would prevent the email client from submitting outgoing messages to the server, while leaving web traffic unaffected. The email server is confirmed working, so the issue is likely a blocked outbound port on the client's firewall.
What should I do if I get this 220-1201 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Same concept, more angles
3 more ways this is tested on 220-1201
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A customer reports that they cannot send emails from their desktop email client, but they can receive emails. The email server is running on the local network. Which port is most likely blocked on the firewall?
easy- ✓ A.25
- B.110
- C.143
- D.993
Why A: Port 25 is the default SMTP port used for sending email. If the firewall blocks outbound or inbound traffic on port 25, the desktop email client cannot establish an SMTP connection to the local email server, preventing email transmission while still allowing reception via other protocols.
Variation 2. A user reports that they cannot send emails from their Outlook client, but they can receive emails. The email server is using standard ports. Which port is most likely blocked on the firewall?
easy- A.110
- B.143
- ✓ C.25
- D.443
Why C: Port 25 is the default SMTP port used for outgoing email transmission. If a firewall blocks port 25, the Outlook client cannot connect to the SMTP server to send emails, but receiving via POP3 (port 110) or IMAP (port 143) remains unaffected. This matches the user's symptom of being able to receive but not send emails.
Variation 3. A user reports that they can receive emails but cannot send any. The email client is configured with SMTP on port 25. The IT team confirms that port 25 is blocked by the ISP. Which alternative port should be used for SMTP submission?
medium- A.Port 110
- B.Port 143
- ✓ C.Port 587
- D.Port 993
Why C: Port 587 is the standard SMTP submission port defined in RFC 6409 for email clients to send outgoing mail. Unlike port 25, which is used for SMTP relay between mail servers and is often blocked by ISPs to prevent spam, port 587 is specifically designated for client-to-server submission and typically supports STARTTLS encryption. Using port 587 bypasses the ISP's block on port 25 while adhering to modern email security practices.
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Last reviewed: Jul 4, 2026
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