throwing a custom exception in a delegate method

Question

I am trying to throw a custom exception in one of the delegate methods of NSURLSessionDateTask.

-(void)loginWithEmail:(NSString*)email Password:(NSString*)password
{
    @try {
        NSURL *Url              =       [NSURL URLWithString:@"Http://..."];

        NSData *PostData        =       [Post dataUsingEncoding:NSASCIIStringEncoding allowLossyConversion:YES];

        // preparing the request object
        NSMutableURLRequest *Request = [[NSMutableURLRequest alloc] init];
        [Request setURL:Url];
        [Request setHTTPMethod:@"POST"];
        [Request setValue:postLength forHTTPHeaderField:@"Content-Length"];
        [Request setHTTPBody:PostData];

        NSURLSessionConfiguration *config = [NSURLSessionConfiguration defaultSessionConfiguration];
        config.TLSMinimumSupportedProtocol = kTLSProtocol11;

        NSURLSession *session = [NSURLSession sessionWithConfiguration:config delegate:self delegateQueue:nil];

        NSURLSessionDataTask *dataTask = [session dataTaskWithRequest:Request];

        [dataTask resume];
    }
    @catch (NSException *exception) {
        NSLog(@"%@", [exception description]);
        @throw exception;
    }
}

- (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask didReceiveData:(NSData *)data
{
    NSData *response1 = data;
//    NSError *requestError           = NULL; // captures the returned error (if exists)
//    NSURLResponse *urlResponse      = NULL; // captures the response returned by the service
    NSMutableDictionary *parsedData = NULL; // holds the data after it is parsed
    NSError *err = NULL;
    if(!response1)
    {
        // If response is nil, connection timeout.
        loginSuccessful = NO;
        @throw [NSException exceptionWithName:@"Connection Timeout" reason:@"No Connectivity" userInfo:NULL];
    }
    else
    {
        NSString *formattedData = [[NSString alloc] initWithData:response1 encoding:NSUTF8StringEncoding];

        if([formattedData rangeOfString:@"<!DOCTYPE"].location != NSNotFound || [formattedData rangeOfString:@"<html"].location != NSNotFound)
        {
            loginSuccessful = NO;
            @throw [NSException exceptionWithName:@"Server Issue" reason:@"Could not connect to server" userInfo:NULL];
        }
        else
        {
            parsedData = [NSJSONSerialization JSONObjectWithData:response1 options:NSJSONReadingAllowFragments error:&err];
            NSMutableDictionary *dict = [parsedData objectForKey:@"User"];

            loginSuccessful = YES;
        }
    }
    //handle data here
}

However, when a custom exception is thrown, the catch block in "loginWithEmail" method does not catch the exception, and my application crashes. Where is the exception propagated when it is generated inside a delegate method? How should I handle it?