fix(block): Improve error handling of SendEmailBlock (#11420)

Currently if the smtp server is not configured currently it results in a
platform error. This PR simplifies the error handling

### Changes 🏗️
 
- removed default value for smtp server host. 
- capture common errors and yield them as error

### Checklist 📋

#### For code changes:
- [x] I have clearly listed my changes in the PR description
- [x] I have made a test plan
- [x] I have tested my changes according to the test plan:
  - [x] Checked all tests still pass

autogpt_platform/backend/backend/blocks/email_block.py

@@ -1,4 +1,6 @@
 import smtplib
+import socket
+import ssl
 from email.mime.multipart import MIMEMultipart
 from email.mime.text import MIMEText
 from typing import Literal
@@ -48,9 +50,7 @@ def SMTPCredentialsField() -> SMTPCredentialsInput:
 
 
 class SMTPConfig(BaseModel):
-    smtp_server: str = SchemaField(
-        default="smtp.example.com", description="SMTP server address"
-    )
+    smtp_server: str = SchemaField(description="SMTP server address")
     smtp_port: int = SchemaField(default=25, description="SMTP port number")
 
     model_config = ConfigDict(title="SMTP Config")
@@ -67,10 +67,7 @@ class SendEmailBlock(Block):
         body: str = SchemaField(
             description="Body of the email", placeholder="Enter the email body"
         )
-        config: SMTPConfig = SchemaField(
-            description="SMTP Config",
-            default=SMTPConfig(),
-        )
+        config: SMTPConfig = SchemaField(description="SMTP Config")
         credentials: SMTPCredentialsInput = SMTPCredentialsField()
 
     class Output(BlockSchemaOutput):
@@ -120,7 +117,7 @@ class SendEmailBlock(Block):
         msg["Subject"] = subject
         msg.attach(MIMEText(body, "plain"))
 
-        with smtplib.SMTP(smtp_server, smtp_port) as server:
+        with smtplib.SMTP(smtp_server, smtp_port, timeout=30) as server:
             server.starttls()
             server.login(smtp_username, smtp_password)
             server.sendmail(smtp_username, to_email, msg.as_string())
@@ -130,10 +127,59 @@ class SendEmailBlock(Block):
     async def run(
         self, input_data: Input, *, credentials: SMTPCredentials, **kwargs
     ) -> BlockOutput:
-        yield "status", self.send_email(
-            config=input_data.config,
-            to_email=input_data.to_email,
-            subject=input_data.subject,
-            body=input_data.body,
-            credentials=credentials,
-        )
+        try:
+            status = self.send_email(
+                config=input_data.config,
+                to_email=input_data.to_email,
+                subject=input_data.subject,
+                body=input_data.body,
+                credentials=credentials,
+            )
+            yield "status", status
+        except socket.gaierror:
+            yield "error", (
+                f"Cannot connect to SMTP server '{input_data.config.smtp_server}'. "
+                "Please verify the server address is correct."
+            )
+        except socket.timeout:
+            yield "error", (
+                f"Connection timeout to '{input_data.config.smtp_server}' "
+                f"on port {input_data.config.smtp_port}. "
+                "The server may be down or unreachable."
+            )
+        except ConnectionRefusedError:
+            yield "error", (
+                f"Connection refused to '{input_data.config.smtp_server}' "
+                f"on port {input_data.config.smtp_port}. "
+                "Common SMTP ports are: 587 (TLS), 465 (SSL), 25 (plain). "
+                "Please verify the port is correct."
+            )
+        except smtplib.SMTPNotSupportedError:
+            yield "error", (
+                f"STARTTLS not supported by server '{input_data.config.smtp_server}'. "
+                "Try using port 465 for SSL or port 25 for unencrypted connection."
+            )
+        except ssl.SSLError as e:
+            yield "error", (
+                f"SSL/TLS error when connecting to '{input_data.config.smtp_server}': {str(e)}. "
+                "The server may require a different security protocol."
+            )
+        except smtplib.SMTPAuthenticationError:
+            yield "error", (
+                "Authentication failed. Please verify your username and password are correct."
+            )
+        except smtplib.SMTPRecipientsRefused:
+            yield "error", (
+                f"Recipient email address '{input_data.to_email}' was rejected by the server. "
+                "Please verify the email address is valid."
+            )
+        except smtplib.SMTPSenderRefused:
+            yield "error", (
+                "Sender email address defined in the credentials that where used"
+                "was rejected by the server. "
+                "Please verify your account is authorized to send emails."
+            )
+        except smtplib.SMTPDataError as e:
+            yield "error", f"Email data rejected by server: {str(e)}"
+        except Exception as e:
+            raise e